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Why Lithium Battery Load Dumps Matter

I have been thinking about and researching lithium batteries a lot over the last three months. One of the things that has jumped out at me is the way the load dump problem is being downplayed by both cruisers and industry players.

Now, before I go any further, this is not going to be a tirade against lithium batteries on cruising boats. I’m totally aware of the compelling benefits.

Rather, I’m going to discuss why it’s so important to install a lithium battery system that will prevent load dumps, and then, in the next article, I will cover how to do that.

Let’s start with a quick overview of what load dumps are.

If any of the following limits are violated¹:

  • Over temperature
  • Under temperature
  • Charge over-current
  • Charge over-voltage
  • Too low state of charge
  • Too high state of charge
  • One or more cells in the battery too far out of voltage balance with the others

The battery management system (BMS) will disconnect the battery; in other words, a load dump.

Bonus Tip

The very words “load dump” are misleading since many BMSs, particularly cheaper ones, will disconnect both the loads and charging sources, and smarter ones will more frequently disconnect the charging sources than the loads, so “charge and/or load disconnect” would be more meaningful wording.

The next thing to understand is what we are typically told about load dumps is salesperson-speak at best, and dangerous at worst.

For example, a common reassurance we get when we ask about load dumps is that they are no problem since all we need to do is install an alternator surge suppressor and then load dumps won’t matter since no damage will be done.

First off, the idea that one of these little gadgets will always and repeatedly protect the alternator and the boat’s electronics is suspect at best, but that’s a different article.

¹Some less expensive and less capable BMSs don’t monitor for all of these criteria.

Load Dumps Are High Risk

The second issue, that pretty much universally gets ignored or glossed over, is how dangerous load dumps are, right up to jeopardizing the lives of the crew on the boat.

OK, that sounds dramatic, but let me give you a couple of scenarios to make my point:

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More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Current (Amps) Requirements and Optimal Voltage
  33. Lithium Battery Buyer’s Guide—Fusing
  34. Lithium Buyer’s Guide—Budget: High End System
  35. Lithium Buyer’s Guide—Budget: Economy Options
  36. 11 Steps To Better Lead Acid Battery Life
  37. How Hard Can We Charge Our Lead-Acid Batteries?
  38. How Lead Acid Batteries Get Wrecked and What To Do About It
  39. Equalizing Batteries, The Reality
  40. Renewable Power
  41. Wind Generators
  42. Solar Power
  43. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  44. Battery Monitors, Part 1—Which Type Is Right For You?
  45. Battery Monitors, Part 2—Recommended Unit
  46. Battery Monitors, Part 3—Calibration and Use
  47. Battery Containment—Part 1
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Matt Marsh

I have not had a lithium-ion bank on a boat load dump on me. (To be fair, I’ve never had a boat with lithium batteries.)

I have had a whole lot of smaller Li-ion devices — lamps, power tools, IT equipment, a solar race car — do this. I fully understand why it’s necessary. But, when it happens, it is annoying at best, and can very well turn dangerous.

The widespread promotion of “drop-in replacement” lithium batteries is, I think, a major risk factor here. A lot of those things are meant for streetlights and traffic signals, and have just been relabelled (not redesigned) for marine use.

A properly integrated lithium-ion system requires a fundamentally different architecture than a lead-acid one. Among many other things, having independent charge and load buses is more-or-less unheard of in conventional systems, but absolutely essential in lithium ones. Simply dropping LiFePO4 modules and a BMS into the same spot as the old lead-acid bank might seem to work, most of the time, but the electrical architecture is fundamentally wrong and so this risk will always exist unless you redesign the entire system. I’ll save the rest for later, in the interest of not front-running part 2.

Ben Logsdon

Instead of a “spoiler alert”, this article needed a “cliffhanger alert”!

Ernest E Vogelsinger

We could have a very lengthy discussion of what is seamanlike and what not – but I have to resent your general approach like “if it can fail it is un-seamanlike”. If it were, no trusty seaman might ever set foot on a boat.

As I see it there is not a single system that cannot fail, simply by principle. As Andy Schell writes (scroll down to his comment) each system we add to the boat increases the chance of something failing – and I am convinced that this risk awareness is driving you to the KISS approach you are absolutely righteous advocating.

But, since we still want to go cruising, and still want to be “seamanlike” in our approach, we should not be as apodictic as to disallow systems if they can fail – this would also include hulls and seacocks, and boats altogether (not to talk about ourselves, even we fail from time to time 😉 )

I like Andy Schells approach of risk analysis – consequence/probability/mitigation. I would see it unseamanlike if we either ignore a risk, or live in hope that a low-probability risk will not happen to us.

Dick Stevenson

Hi Ernest,
I love being introduced to a new and useful word: apodictic.
Thanks and appreciated,
Dick Stevenson, s/v Alchemy

Michael Feiertag

Yes! Thank you.

Matt Marsh

Risks exist, and can never be completely eliminated. A large part of seamanship is about assessing those risks, and mitigating them before they have a chance to become disasters.

If a risk is unavoidable, then seamanlike conduct requires us to have contingency plans in case something does go wrong.

If a risk comes from bad design, bad engineering, or bad installation, and would not be present if things were set up properly – as is the case here – then I think it is indeed unseamanlike to accept that risk; we are obliged to mitigate it.

Andy Schell

The question is how far do we need to go to mitigate it. In Part 2, John advocates for external BMS systems only for lithium, or go all the way back to lead-acid. I think in some applications, that’s unnecessarily too far.

I think there’s an acceptable level of risk with a properly installed, internal BMS system. The benefit from accepting that risk is vastly improved performance on the electrical system, which is why you accept that risk.

So we can look at this in three ways if we insist on lithium batteries:

  1. Blindly installing a drop-in lithium system and ignoring the risk. UN-SEAMANLIKE.
  2. Properly installing a drop-in, internal BMS bank and reasonably mitigating the load-dump risk, and accepting what we can’t mitigate due to the inherent design in exchange for the better performance. I’d argue this is NOT UN-SEAMANLIKE.
  3. Going all-in and installing an external BMS, fully protected system with a lead-acid buffer bank running essential electronics. FULLY SEAMANLIKE.
Stein Varjord

Hi John,
From what I see, option 3 (separate 3,2V prismatic cells with an external BMS) is normally significantly cheaper than drop-in batteries with similar quality cells and a dramatically inferior BMS system. In reality, we pay a ridiculous overprice for a box that hides that they have used cheaper components.

If we go for ready made batteries from Victron, Lithionics and Mastervolt, they have great components inside, (some of these do not have the BMS inside). If we as consumers buy the same Winston cells they have inside, from reputable dealers in Europe or the US, plus state of the art external components, we would still end up far cheaper.

With option 3, separate cells etc, we do need to pick the right components, install connect and configure them, perhaps do cell balancing and some more. That might be seen as an extra cost, but these days this has become more like using Lego than needing an Electrical Engineer. It’s still not super easy for the non educated, but the exact same is true for options 1 and 2. We need to match the boat and all its relevant units to the drop-in battery too. It’s not really that hard, if the batteries are good, but it absolutely has to be done. True drop-in lithium doesn’t exist.

As long as we go for 12 or 24 Volt systems, good components are supplied by many different companies. If we want 48V or higher, which is interesting for power hungry boats, (we often use 96V) it’s considerably less easy to design the system, but that can also be done by an amateur with some interest. For our commercial electric drive boats we only use separate cells, also with lead acid. Batteries (more than one cell in a box) are far too fragile and far too expensive.

Stein Varjord

Hi John,
Good points. I also think insurance companies will increasingly make a point about DIY installed lithium batteries. Not because DIY installs of lead acid batteries are better, but because they have heard the words “fire” and “lithium” in the same sentences. They choose the easy way out and ignore that phones, laptops etc on the boat are far greater fire risks than LiFePo4 cells. Not even mentioning the wiring harnesses most boats have… Still, we just have to accept that the insurance companies make their own choices.

Orwell is also a fair association when it comes to cell trading. However, there are Winston costomers that buy far larger quantities than Victron et al. Some of these get the same deals, if they ask for it. The cells should ideally be from a single batch, preferably continuous series numbers. Then they need to be checked to be sure that they are actually matched, no flaws. Equal capacity, resistance, etc. None of this is available via AliBaba etc, of course. However it is probably available via the likes of Electric Car Parts and Ocean Planet Energy in the US, and via in Europe.

Either way, the systems need to be both designed and configured right to give the right properties. Buying ready made solutions from Victron solves that by throwing a pile of money at the problem, while at the same time giving warranties and quite smooth installation and operation. It might be the best deal, for many of us. Not for me, but I’m a poor nerd… 🙂

Richard Phillips

I have not had a lithium-ion bank on a boat load dump on me” – being pedantic (but on a point where there is frequent confusion) please install LifePo4 not Lithium Ion – much safter.

Frans Muys van de Moer

So true. I never understood why people would set for a combined load and charge disconnect safety topology.
To my mind it is just plain the wrong solution.
Separate charge and load disconnect is the way to go, add a sound alarm that warns if the low voltage is approached and your are done.
I use relays with manual override, that could be another extra safety measure.

Henri Bergius

We’ve had LiFePO4 on both our previous and current boats.

On the previous (25ft weekend cruiser) boat we had a cheap Chinese drop-in battery with a internal BMS. There we experiences a “load dump” once, caused by me mis-installing a battery monitor, and drawing the battery too low. We were anchored and this happened in the early morning hours, meaning that both the anchor alarm, and the anchor alarm were suddenly off. Not nice, but also not super dangerous in the place and conditions we were in. In the morning we sailed back to marina, plugged the boat in, and figured out what was wrong with the battery monitor. Didn’t happen ever since.

For our current boat (31ft full keel heavy displacement double ender), we went with a all-Victron setup where the BMS is external, and both chargers and loads can be disconnected separately. The load dump that happened with our old boat certainly played a role in this decision. But also the new boat is a lot more heavy in electrics, for both navigation equipment, and especially for post-COVID “boat office” requirements.

Most of our chargers are coordinated by the BMS using Victron’s DVCC setup, so the risk of overcharge causing a disconnect is pretty low. Alternator is connected to the starter battery, and only charges house bank via a DC-DC converter. If we had an externally regulated alternator, I’d get one of those Wakespeed boxes and integrate it also with the Victron system.

Right now we only have solar, alternator, and shore power. We’re thinking to add wind at some point. It looks like at the moment Superwind is the only manufacturer that makes a wind generator that has a controller that is fine with a charge disconnect (the charge controller is powered by the wind gen, not the battery). But for the moment we’re having issues figuring out good placement for the generator, so that’s off until we do some rigging changes.

Henri Bergius

Indeed. And obviously was the reason we went with an external BMS with the new boat. A bit more wiring and thinking needed, but should be a lot more reliable.

Michael Albert

Full disclosure- I don’t have Lithium yet- I’m 4 years into my lifeline AGM bank and probably will consider Lithium next.

This past summer we were skirting the edge of the Chesapeake bay Elk River ship channel nearing C&D canal. Lots of boat traffic, tug and barge around the bend on AIS, watching depth sounder as we stayed just out of channel with not a lot of room. And then everything 12V went dead. Autopilot, plotter, depth, fridge, etc.
Luckily it was daytime and very benign sea conditions. Scramble to hand over helm to my wife, pull up Navionics on iPhone and hand it to her, and dive into the issue. First order of business- inspect batteries and engine room and make sure no electrical fire or evidence of a short anywhere.
Then, 15-20 minutes with a multimeter helped me figure out the culprit- the original analog ammeter wired into the Tartan 40 electrical panel had failed internally. All 12 V electricity went through it after the main breaker.

Quick bypass of this (which is a permanent fix) and everything was powered back up. And luckily the beer in the fridge was cold as I needed one. We continued on up to NE for our summer cruise.

So the lesson is- this was not a lithium fault, and because of that was an easy mechanical fix as I knew the batteries were fine- they always are with lead acid. No electronic gremlins to debug. And it was as easy of a scenario as there could be- but could have been a lot tougher like exiting the canal onto DE Bay at 4am in the dark the next morning, tracking ships on radar and AIS in full darkness.

So your article resonates deeply with me- I’ll let my bank die and technology mature even more before changing over.

Hans Vernhout

We once had a lead-acid starter battery explode when leaving Scheveningen harbour in the Netherlands. 7Bft and gusting, we were just able to sail free of the breakwaters (returning to the dock was no option). So ‘load dumps’ (with lead acid batteries (although rare) do occur and can lead to challenging situations.

Bottom line is that you should prepare for the worst. All technology can fail, just as everything else on your boat. Even some big seagoing ships (with redundant systems) do have total blackouts.

I agree with your observation that we tend to sail more aggressive with all our advanced navigational systems and loose some of the practical skills to do without them, but that – in my opinion – is the real problem to be addressed.

Of course a well designed power system on your boat and a plan B (and C) can minimise the risks, but not taking all the systems on board (batteries are just one of them) for granted during sailing is just part of good seamanship.

So unless catastrophic problems with LFP batteries appear to be far more common than with traditional lead acid setups I think it’s our (lacking) skills and not technology that’s the real problem to be addressed.

Ernest E Vogelsinger

I’m not using Lithium, and most probably will never have one on my boat, but nevertheless I’m more than curious about your ideas for a solution. I will hold back mine for now 😉

Richard Phillips

I think this somewhat over-states the difference.

With Lead Acid, if you over discharge repeatedly you will permanently damage the battery. With LifePo4, if you over discharge (to a *far* lower SOC) you will permanently damage the battery. In both cases you can fit some electronics to prevent over discharge.

And of course both types will be damaged by overcharging – in the case of lead acid it can be very dangerous gassing which has destroyed many boats.

Yes, the detail of how much damage and thresholds of harm are very different – and LifePo4 *must* have high voltage protection on charging because of the risks of entirely killing the bank.

But on the load side it is perfectly feasible to bypass the BMS for essential loads and perhaps have a low voltage warning so you know there is trouble.

Or, as Temptress does – have a small lead acid battery alongside a large LifePo4 bank to buffer the loads and prevent the consequences of the sudden shutdown.

Torsten Hansen

Excellent article, looking forward to your next installment.

The two scenarios that you describe would be bad, very bad, but significantly less so if your system was set up to warn you of the impending disconnect. Even better if it used separate charge and load busses and included a backup feature.

Such systems exist. We chose the X2 BMS from Battery Balance in Sweden to be the brain of our battery bank and I encourage anybody interested in large lithium systems to give it a look. From the ground up, it is built by sailors for sailors.

As a matter of full disclosure, I should mention that I have no connection whatsoever with the company beyond that of being a customer.

Douwe Gorter

Hi John, I believe the comments were made in good will but if the above is really worrisome to you than I suggest you either close the comments on this article and only open the comments again once the next article is published. Hopefully the next article does provide the definitive answers to the issue. Alternatively you could have opted to address the problem in a more concise manner and provide the answer to the problem in one article.

Richard Phillips

Do what you want, but we will have a way better discussion if we all hold our ideas for the upcoming solution article.”

Or maybe the next article will be *even better* if you get to hear various ideas from your fans right here; possible there might be a few things you had not thought of!

Rob Gill

We’ve had LiFePO4 batteries from MasterVolt since 2016. They allowed us to remove and not replace an obsolete Fisher Panda generator and four large end-of-life AGM’s. This took over 300Kg out of the back of the boat, with beneficial sailing results.

Cruising in the SW Pacific, a well kept secret (by the Tourist Board) is that beautiful Vanuatu, even in the dry season, can be overcast for days on end, meaning poor solar output. On our 2017 visit, to save running our engine at anchor I would often run the battery bank below 40% capacity as we are able. At that time we had old and inefficient water-cooled refrigeration, that was a continuous power drain in the warm tropical air and seas.

After being on the island of Efate for about two weeks, I noticed the system had load dumped as it was set up to do (at 30% SOC). It was a simple restore once we figured out what had happened – not so easy to diagnose until you have experienced it once.

I won’t go into why this wasn’t an issue in our case (apart from being at anchor) to avoid front-running the next article, which will be interesting.

Michael Feiertag

I am curious to know how LiFePO4 batteries allowed you to eliminate a genset, as you eventually need to recharge the bank. Did you add a charging source?

Eric Klem

If you look at it on a system level, I think there are definite advantages to a storage device that is less sensitive to its charge level and that can accept charge faster. An example of the benefit of the first is for people who weekend with their boat and leave it on a mooring. With lead acid, if you draw down to 80% over the weekend, now you have the conundrum of whether you just leave it and accept some sulfation or whether you run your engine or genset for ~4 hours to get back to 100%. Before solar was easily doable, I would have jumped at something like lithium but solar has largely made this a non issue.

In any dynamic system, there is always benefit to having your accumulators not be rate limited as then time spent charging and discharging those become really important. With lead acid, most people will find that their engine does a good job of charging in the morning while getting underway as they are probably below 80% SOC but if they are going to motor for a while, it pretty quickly becomes an ineffective charge source due to the self limiting nature of lead acid batteries as their SOC rises. A boat with lithium can take full advantage of that 2 hour motor with the alternator outputting at full output the whole time so the total amount of energy generated can be way higher. You might not need it right then but getting that extra 15% SOC may really help when 2 days later you are sitting at anchor and it is cloudy and you aren’t planning on motoring anywhere but the next day you are and you just need to make it there. You can of course also put on a bigger alternator if your engine is up to it. If you go big enough, you can actually turn your main engine into an effective generator but you do need to be careful to do it right although it should be easier than the rest of the lithium puzzle.

John’s point about the weight and size trade-off is right as well. Because our charge sources are pretty irregular in nature, more energy storage means you can often get through a lull between charges and not be forced to crank up a fossil fueled charge source.

To me this is another one of those use case questions. Modeling this sort of stuff is a bit tricky and making the proper trade-off in a completely rationale sense is not a given although I know a lot of people would love to never think about SOC for lead acids. If we didn’t have solar, we would be killing lead acids pretty quickly and I might be looking to make a change the way we use our boat. But for our modest energy usage, going lithium wouldn’t make a big difference but I can see it making all the difference for others.


Rob Gill

Hi Michael,
The answer is entirely that our LiFePO4 batteries charge to 100% quickly whenever the engine is running, as articulated well by Eric. This more than replaces the power we needed from our old generator.

We have 3×180 Ah MasterVolt batteries. MV recommend no more than 30% supply side current for maximum battery life, ~ 160A. The most supply current I have seen in the BMS is 160A on a very sunny day in NZ (our solar gain is very high), so no storage opportunity is wasted.

We have (and had) 650 W of removable solar panels, but with our original water-cooled refrigeration and AGMs, we had to run our generator once a day, and more on cloudy days. It took forever to reach 90% charge and we never got to 100% out cruising – never liked the noise.

For completeness:

  • On the supply side, we replaced the factory fitted 60A alternator with a new 130 A on our Volvo D2-55hp engine. We are regularly putting 100 to 120 A into our LiTePO4 batteries motoring (80 to 90A at anchor).
  • On the load side we recently replaced our horribly inefficient water cooled refrigeration with smaller air-cooled units. This has halved our daily power use.

Now, on cloudy days motoring for an hour, or occasional top-ups using the engine alternator is more than enough.

Could we have achieved the same with AGMs? With the refrigeration upgrade and hindsight, yes possibly. But we would spend more time with an engine running.

Stein Varjord

Hi John,
The dramatically higher charging efficiency of lithium batteries actually make them add more charging power. It’s already been mentioned, but the degree is often underestimated. If a boat installs a good lithium system, (most on the market are not) same V and Ah as the lead acid batteries it had, but changes absolutely nothing else, it can expect to get roughly twice as much useable power from the solar panels. So changing the batteries gives the same result as doubling the solar panels. The batteries are no actual power source, of course, but it can certainly feel that way.

Peter Haeussler

I needed a new battery bank on a newish-to-me boat a year ago, and in many ways this singular issue was the tipping point that stopped me from going lithium. I’m glad you’ve fingered it (Well, Rod Collins/MarineHowTo is where I learned about it.) But, it seems likely that I’ll want to drink the lithium Kool-aid in the future. In the meantime, We took a bunch of steps to get the boat closer to ‘lithium ready.’ These included: upgrading undersized and variable sized battery/backbone cables, installing a Wakespeed WS500 charge controller on the high-output alternator, installing proper fusing in the backbone of the boat, installing useful battery monitors, and installing a Sterling Alternator Protection Device (which seems more like a life jacket than a solution to falling overboard). We ended up getting Firefly carbon foam batteries, and so far they have been awesome and trouble free and sustain deep discharge.

A few issues still stand in the way of lithium on our boat: 1) I’m in Alaska, and not being able to charge below freezing can be an issue. 2) Separating charge and load busses would be a pile of work involving challenging cabling runs related to boat structure. And 3) I’d need to fork out yet more dollars for a new charger inverter that supports lithium.

In the one year since we made our decision to not go lithium, its been interesting to see what has changed. It seems there are now a handful of BMSs that can communicate with an alternator charge controller. The price of LiFePO batteries has continued to drop, the use of the batteries is much more accepted, and now some insurance companies are probing the quality of lithium installations. Anyway, I’ll look forward to seeing John’s favorite solution. Mostly, I don’t want to be a lithium battery systems expert, but I’d rather go safely cruising and know more about where I’m going and where I’ve been!

Yannick Piart

Peter, although I’m not cruising in freezing areas I’ve added heating pads to the LifePo4 batteries I built last year (just in case!). Maybe an option for you?

James Rambo

Hello John,

We experienced a load dump at night on our boat that we recently sold. The setup was a Victron lithium smart battery with external BMS and separately controlled charge and load. My wife was at the helm and everything went dark as the BMS cut off the loads. She says, “Honey, I think something is wrong.” Since I participated in the design and install, I immediately knew what likely happened and yelled towards the companionway, “Start the engine, start the engine right now!” The alternator kicked in, started charging, and everything started turning back on. In the post trauma relief, the boat started heading off course until we realized the auto pilot was back on but we still had to click it back on auto. The cause was the battery monitor (smart Victron) falsely assuming the battery was at 100% charge earlier in the day. Although I followed the typical Lithium suggestions in the manual, I discovered upon further study that the monitor only guesses when the battery is full using several factors. One of the factors is voltage level which we had set at recommended levels, however, in certain cases with lithium and solar charging where cloud cover or other factors can cause intermittent, fluctuating charge levels, the monitor thinks the charge is slowing because the battery is full. Lithium in particular reaches higher voltage levels quickly at perhaps 50% SOC so the combo of slowing charge and voltage above threshold flipped the monitor to 100% when it really was closer to 50%. Of course we had great sailing conditions that night and saw no need to charge when the monitor said we had plenty of charge. The simple solution which Victron actually suggests in a youtube video is to increase the voltage threshold for lithium. I’ll never forget to make that adjustment on the next boat which will still definitely have lithium!

Philippe Candelier

ABYC as part of its recommendation when service battery bank is made of LiFePO4 recently requested that a secondary service bank must be installed. The second bank can also be LiFePO4.

Andy Schell

My overall point: these problems related to load dumps are teachable and can be overcome using the principles of good seamanship. Paradoxically, the problems these systems create forces us to think about seamanship in a more fundamental way that you describe. For example, your coastal entrance to Halifax – knowing there is even a slight chance of load dump creating an electrical system failure might force us to consider a different, more conservative tactic on entering the harbor. Now we’ve gained a higher-performing electrical system overall, and become better seaman in the process by understanding the downsides. Assuming people will tend toward relying on the tech as they always do is probably true…but it’s also cynical. More detailed reply:

  1. Load dumps is a very poor word for what these various scenarios describe. I am guilty of misunderstanding the term myself and I’m waist-deep in research here. “Total Electrical System Shutdown” seems a better term, or at least way of understanding it.
  2. With that assumption, you can then weigh the risk/rewards of using such a system. I think your blanket statement is misleading and unfair in the context of lithium: “So if we build a system that increases the chances of something unexpected happening at a bad moment, even just a little, that’s just…plain…bad…seamanship.” We do this all the time! This is nothing new with lithium, it’s just yet another example of how adding systems of ‘convenience’ create more and deeper problems to solve when those systems fail. There is a MUCH larger conversation to be had around this and how it relates to building on a foundation of fundamental seamanship in the first place, but we’ll save that for our next podcast. My point is if you literally applied that statement to every system on the boat you’d not have roller-furling, winches, wheel steering, electrics of any kind, and on…
  3. There should be included in this discussion on risk the likelihood of said risk, and the consequences. It’s the old black swan theory – tiny risks with world-changing consequences. From anecdotal experience with many friends who have even cheap drop-in lithium installed, the likelihood of a full system failure is small, and the likelihood of that failure happening in a crucial moment as you describe is even smaller. It’s not to say we ignore it. My point is I think in a lot of case that subtle added risk is worth it, if you mitigate the downside. The tradewinds example – that same autopilot failure and jibe consequence can occur for any number of reasons beyond a load dump in a lithium battery. Worse yet is if the pilot computer malfunctions and veers off course while the unit is still engaged and requires shutting it off before you can regain control. And on…
  4. I believe what you’re assuming is that most people don’t think about these kinds of consequences, and there I would agree with you. And if you want to build a truly “set and forget” electrical system, then lithium may not be the best choice. But if you take the time to learn the risks, assess them, mitigate for them, and finally accept the tradeoff of elevated risk for the ample rewards even a simple lithium system offers, then there’s nothing wrong with that. Though I assume this is where your next post is going…
Alastair Currie

Apologies – comment is not on load dumping. Risk Management is a whole discipline that regularly gets misapplied. The interactions of hazards, consequences and probabilities (risk) can take folks down rabbit holes. Having said that it can also be quite simple if most of the probability is ignored and the focus is on Hazard and Consequence without wondering about probability.

Also be careful about assuming most folks don’t think about consequences, the point being made is risk normalisation. This is a known psychological process, or Normalisation of Deviance as it is termed in psychology. An infamous example, from people who thought intensively about risk and managing it, was the Challenger Shuttle disaster. They were so used to launching outside the specification of the O rings, that when it really mattered, everyone convinced themselves that it was okay to go – classic risk normalisation. Then we have the rest of us, non rocket scientists, who are doing our best to have affordable systems on boats to enjoy a leisure (mostly) activity, free from the prescriptive controls and barriers to hazards, applied to the commercial world.

It is a learned behaviour, Normalisation of Deviance, and it can be unlearned. As sailors who want to venture far, it is a mindset that needs to be guarded against.

Andy Schell

Great points and thanks for putting actual language to one of the points I was trying to make.

Ernest E Vogelsinger

Maybe I misunderstood you – what I take from this comment is that you do not primarily see it un-seamanlike to install such a system (every system can fail), but to know this risk and prepare no mitigation against it. If it is this what you’re talking about, I’m on your side.

Ernest E Vogelsinger

You should add a “like” button to the comments. I would like to click it here 😉

Ernest E Vogelsinger

I’d like this Comment as well 😁

Andy Schell

I think we’re saying the same thing. I didn’t say, nor did I mean to imply, that you can ‘ignore the problem and hope it doesn’t happen.’ Will save further comments for Part 2.

Something else though I wonder, and which there probably isn’t an answer to. How prevalent is a load dump in a properly installed system? Reminds me of the hitting a container at sea problem – are we worrying about an issue so rare as to negate the need to worry about it? I doubt it in the load-dump case, and we probably won’t ever get useable stats on it, but still makes me wonder.

Rob Gill

Interesting and useful topic, discussion and valid industry call-out by John.

And excellent question from Andy about the incidence of load dumps “in properly installed systems”. But perhaps we would also need to consider the incidence of load dumps within spec, and the incidence out of spec. And then whether that spec is from an established marine electrical supplier like MasterVolt or Victron. So many variables to make an informed decision.

As Andy articulated, issues with technology happen all the time at sea. Anticipating and dealing with this is part of vessel management and seamanship. As a professional navigator for eight years on ocean-going ships (probably less than two years of actual sea-time) we broke down (not-under-command) about four times due to system/engine failure, including one complete electrical blackout I can remember.

One event included being unable to stop our engine as we headed towards a fully laden oil barge tied up in the busy distributary of the Rhine at Rotterdam.

We also had three serious ship fires on ships I was on, one caused by a new bow-thruster deciding to start up of its own accord mid-Pacific (only ship I sailed on with one). Our fleet had over 30 ships so not a small player.

Yesterday I was chatting with a good friend, sailor (circumnavigator) and highly skilled electrical engineer specialising in testing and troubleshooting high-voltage installations and their control systems. He had just returned to NZ from Malaysia where he had been asked aboard an ultra-modern drill ship (the kind that can maintain station to within metres in a full gale) which suffered a six hour electrical blackout including their electrically powered thrusters. Luckily this was on passage (so not drilling) in the Malacca Straits.

The ship owners wanted to understand why their expensive Siemens control and switching systems failed. Poor initial design (not resilient electrically), poor installation (insufficient fail-safes), poor maintenance (some fail-safes over-ridden) and poor response by the ship’s delivery crew (ignored warning), culminated in a large flash and bang – sorry, I can’t be more technical than that.

So issues in the marine industry are not limited to recreational use and in our case we have had one load-dump from our three MasterVolt LiFePO4 batteries in six years (caused by my human error). We are under one-third of our expected battery life cycles.

This is of course only one data point, but I like that this technology has performed exactly within specification so far. That is something we can mitigate and manage.

Andy Schell

Thanks for emphasizing my point about “properly installed systems.” There has to be some baseline by which we measure the incidence of load dumps (and all failures for that matter).

Whitall Stokes

Great topic John. On my Open 50 on autopilot I thought about this BMS cutoff risk a lot with my LiFePO4 setup. The risk of crash gybing during a Southern Ocean gale rang through my head as I pondered the strength of my gooseneck. I will hold off commenting on how I got around the risk for part two.

Great stuff on risk management.

Eric Klem

Hi John,

I totally agree that these types of load dumps are not acceptable from a safety standpoint if they have any reasonable chance of happening. I have no experience with lithium on boats so no experience there but like you, I have never had a lead acid system fail me in this sort of way. I have lost part of the system by tripping a breaker but I have never lost the main battery fuse so as long as the critical electronics are not all cabled together onto the same circuit, I think it is pretty unlikely. The only failures I have had with lead acid are in electric vehicles where if you pull 1000+A for a long time out of string of GC2’s in series, any posts that have high resistance will melt and fall into the cells making a really cool noise. But this is not a use case that compares in any way to boats.

My issue with lithium is not that it can’t be done safely as you will cover in part 2, it is the knowledge, money and effort required to do it right. From an opportunity cost standpoint, I see many other areas where we could increase our boat performance or enjoyment more for the same resources but I can also see a day where lead acid is no longer the right answer for us. The companies are putting out products that take ever more knowledge to install, use and maintain while often not properly documenting it and if it were only in the area of batteries, it might be manageable but we also have it in electronics and many other systems. Just looking at a lot of the boats I see, most boat owners and often professional yards are failing miserably spec’ing, installing and maintaining much simpler systems including basic fusing. The current state of most products on the market look to me like if instead of buying a full engine, you bought a short block and then were responsible for buying the fuel system, cooling system, etc yourself from other vendors piece by piece. You have already written on the obvious solution to this and it is good to hear that several of the readers here have done that. There are always going to be the people who are capable of doing this well themselves but I suspect they are a pretty small minority. I think about this growing complexity a fair amount with my work as we design products that push our field and it is a super hard balance as increasing features and performance often necessitates more complexity. Can you imagine going back to a land-line only, no PC and 1980’s cars world? We have made huge progress in technology but being an early adapter can be very problematic.


Eric Klem

Hi John,

I totally agree on being requirements driven as I know you have written about before.


Kevin Towers

Having spent the last 20 years designing electronics for industrial vehicles, I wanted to clarify the definition of load dump. Load dumps happened when the load (battery) suddenly disconnected from the alternator. This typically happened due to corrosion of wires or loose battery terminals.

When this happens, the alternator voltage could spike over 85 volts – this is on alternators protected with voltage clamping devices. Older unprotected alternators could reach over 150 volts!

I think we should reserve the term “load dump” to describe this failure only. “Low voltage disconnect “ is a better description for batteries turning off their outputs.

Richard Phillips

Over at Sailing Temptress – Clark has some interesting thoughts on *combining* lead acid and LifePo4 batteries to get the benefits of both without the downsides. His approach entirely avoids the load dump problems described here (the lead acid continue to service the load if BMS shuts down). He has several videos on this, but this one is I think a good overview of his ideas.

Personaly, I just have an emergency bypass switch so that the house load can be take direct from the battery and *not* via the BMS. Obviously this needs using with care, but most load dumps are because of charging issues.

I do think the load dump issue needs thinking about, but the benefits of LifePo4 batteries are so huge that it is worth working around the load dump issue rather than stick with the horrible inneficiencies (and dangers) of Lead Acid.

LifePo4, LED lights and Photovoltaics are, taken together, utterly transformative technologies for boats.

Peter Rowland

Like Clarke and Emily on Sailing Temptress we have a hybrid system. Alternator charging goes to an AGM engine battery, actually two and then via a DC/DC Victron charger to the LFP hybrid. In a year of coastal cruising and no shore power we have used the DC/DC charger twice as solar provides nearly meets all our needs. Solar is connected directly the LFP/FLA house bank. If the Daly BMS shuts down, we have 85Ah of FLA to keep us going supported by solar whilst we sort the problem out, or use the DC/DC Victron in power supply mode. This removes the risk of the BMS shutting down the house systems.

One year in, no problems and we now have sufficient power to cook for 2 days on electric before we need to think about a charge to the house bank. 300w solar isn’t quite enough with a deficit of 30Ah a day. We will add more solar next winter leaving gas as a standby method of cooking. Handy as there remains a very real shortage of gas cylinders in the UK, though why I really don’t know. We exchange cylinders rather than fill, but empties fill the chandlers and no one is collecting fast enough to meet the demand. LFP has been our savour with either a mix of full electric cooking and we use the kettle a lot drinking tea, and the English do.

George L

Misunderstandings happen easily and are a cost of communicating. It’s a fact of life and there’s no point to get hung up about it or take it personal.

you clarified what you meant to say and that’s all there is to it.

looking forward to part two as we are in the middle of getting ours designed. And yes, Mikael from battery balance is a great resource. We are getting our batteries from him.

Yannick Piart

To make it quick I’ve built my LifePo4 system last year and the simplest and cheapest option I found to hopefully make it fail safe, is that I have installed a small lead acide bank in parallel of my lithium one. I sized it to last one night with ultra minimal electric needs turned on so it can take over a total failure of the lithium until sunrise… when solar should be back to support it a bit hopefully.
I will be reading with great interest the solutions you have as I scratched my head a lot on this a few months ago.
Fair winds!

Alan Stevens

OK, John, I will hold off untill I read the next one, but oith scenarios you posit are extreme. The first one is atually wrong if your wiring is setup correctly. As long as you have charhing current from the alternator, and you have a load from the instruments, you have a circuit. It doesn’t matter if the batter cuts out,

And the second scenario, your battery shuts down due to low voltage?, That would take some time, you hadn;t noticed that you were not charging? If the was a lead acid, you would have been out of power much sooner.

Petri Flander

Hello Alan and John,

I noticed the same thing, Scenario 1 doesn’t necessary play out that way because alternator stays connected and there could be enough load to mitigate the load dump spike. Or not. But it doesn’t really matter on the big picture, BMS cutoffs can, and will play tricks if we do not plan ahead, so example is valid anyway.

Also, scenario 2 brings out one thing that I haven’t thought before: Brownout.
In daytime, when it’s shiny and PV tops up the bank and BMS disconnects, and if right after that it gets cloudy, now the PV alone cannot feed needed 18 amps to autopilot, fridge and laptop. There will be a voltage drop, ie. a “Brownout”.

That is a bit fuzzy scenario, because it is dependent on BMS disconnect voltage, load, PV output and BMS reconnect time. But it seems that on “laissez-faire-lithium-system” it can happen, and is another argument against that because “smart system” never gets BMS disconnect because it directs the load sources to go float voltage.

And yes, “float voltage” is a bit tricky concept on lithium systems. I’m not aware of any system that actively adjusts the float voltage so that there is no more any inbound current to already topped-up lithium bank, and instead all charge current goes to loads…

Frederick Gleason

LiFePo disconnects are inevitable as the batteries get older, however the system can and should be designed to protect electronics from transients and the alternator. Obviously a dual bus system would be best, but having a backup/starter AGM or FLA battery to help serve as a load dump, and WS500 regulator does help.

All of this seems to be a bit “Tempest in a teapot”, although by now there really should be a more standard and accepted marine solution. The marine/van situation is not a small market.

Trojan had drop in LiFePo that had a BMS with configurable canbus connection but that battery was withdrawn for some reason.

Kevin Millett

I hope I’m not repeating anything already covered but I did a fast scan and didn’t see anything about “pre-charge” as a another failure point. My Lithionics initially came with internal BMS’s (very bad idea if you ever need to return a failed BMS!). No one mentioned the option of “pre-charge” to me. When I was initially working out stuff it was in the daytime– So my solar, which comes on gradually, was always pre-charging the system. Thus when I turned the batteries off and then back on there was no problem. Well, working after dark, turn the batts off and they won’t restart without disengaging the inverters. Took a while to figure out where the batts thought there was a fault…( Once again solar had been hiding this issue too)
Much more frustrating, however, over the next few days my batts depleted rapidly. What gives? Oh, no solar coming in. Turns out switching on the batts without solar charging (after dark) caused a surge that smoked all the fuses in my Gensun controllers. I emphasize that I didn’t find this weakness until I had already made a Pacific passage. That would have been very inconvenient at sea. Sales response– “Oh, you should have ordered pre-charge option…).
Why would this even be an option vs standard?

Robert Shook

Avoiding load dump blackouts is avoided simply by running core navigation, autopilot, etc off an AGM battery that is maintained by the LFP bank with a dc-dc charger/converter.

My boat’s main bank is 48v LFP. Most of my house voltage (lights, nav, comms, windlass, etc) is 12. I have one AGM battery and 2 48-12 dc-dc converters in parallel to keep it charged. I also have the ability to quickly switch solar charging to 12v in case something happens to 48v.

This isn’t “how to prevent load dumps”, more about redundancy that would negate them. It seems more relevant here but I can delete and post it on the next article if you disagree.

Stein Varjord

Hi John,
This article contains a quite simple message, which is indisputably correct. I fully agree. Some may from that think I’m negative to lithium. In reality, I’m a bit of a fan boy, but I understand enough of the tech to strongly dislike the majority of what is offered on the market.

I don’t sell batteries or services, but I work with large battery packs in electric propulsion tourist boats, both as a skipper and a techie. We have mostly lead acid packs, 43 boats now, from 50 to 200 passengers capacity, but are also (on my initiative) looking at Lithium systems.

The issue this article points at is not that the batteries or BMSes are misbehaving. They’re doing what they were made to do: Protect the cells from damage caused by a misbehaving boat system. The problem is that battery pushers have established the term “drop-in lithium battery”. That indicates that we can lift out the lead acid battery and replace it directly with their “smart” lithium battery. That claim is ALWAYS a LIE! It can work ok for a while, but it will fail.

The LiFePO4 cells absolutely need to be protected by a BMS. It needs to be able to cut both charging and load sides, (preferably not simultaneously). It must be allowed the ability to do something we cannot accept that it does. That sounds like a disqualification of lithium in boats, but it isn’t.

I’m not going to step into the topic of the next article here, but the solution to the above problem is that the BMS must be able to communicate what it’s observing and give warnings well before it takes any actions. We can use those warnings to adjust and remove the problem so the BMS doesn’t have to do anything.

We can check with any lithium battery system we might be tempted by: Can the BMS (etc) communicate properly with other control units we have in our system, so that they, without any action from us, can react to that communication and adjust their behaviour?

If yes, great! We’ll have a far more reliable power storage than most, no matter what chemistry they have. We most likely have found a good candidate! In reality, almost none of the present drop-in offerings can do this well enough. An integrated BMS, inside of the battery box, is never a good idea. It could still absolutely do a good enough job, (albeit never excellent), if it was well made, but it rarely is.

Charles Hendricks

We’re on a large power hungry cat that we cruise full time on. This year we happened to be Ft Lauderdale and talked with three well known installers about lithium. We gave them our requirements (safety, reliability, redundancy, and price in that order). Our quotes were all around $38,000 for a 1000ah system.

We already have a couple thousand watts of renewable (solar and wind) so these quotes only included upgrading the alternator charging systems and adding a charger for shore power/generator.

We currently have a large bank of Firefly batteries and have never had any issues with power even though we have a 50” TV, clothes washer, DC watermaker, ice maker, microwave, multiple computers, etc.

Taking a hard look at the costs and benefits, the only things we could come up with as a reason to switch was if we ditched propane and went to an electric galley and ran air conditioning and the water heater off the batteries.

Are those things worth $38,000? Not for us. That kind of money buys a lot of generator fuel.

If we ever buy a new boat and a robust lithium system as an option, we’ll think about it but for us, a retrofit just doesn’t have advantages worth it.

Another benefit? We can get a 12v lead acid battery pretty much anywhere in the world while we explore.

Garry Crothers

I look forward to the next article. It is an area of my own DIY install I’m a bit less confident about. I have separate load and charge bus solenoids driven by 123SmartBMS and separate low and high voltage alarms (BMV712) set before the BMS trigger points. The way I dealt with High Voltage disconnect causing a Load Dump is that the BMS powers down the Balmar external regulator. This has happened a few times when I’ve not heard the high voltage warning and not switched off the alternator by its Manual on/off switch. So far I haven’t had any issues but I’m still not confident in that being enough to stop high voltage spkes destroying equipment. I guess that the separate load bus solenoid being unaffected allows the spikes to be moderate by the batteries.

Furthermore, regulator shutdown to protect against load dump doesn’t address the low voltage disconnect issue leaving me without any instruments, VHF or lights.

To this end I will be installing a lead acid battery in parrallel. I just haven’t worked through any possible implications this may in itself bring, or exactly where in the circuit is best to install.
Just another job on my never ending list ..

Bring on the next article. This has certainly created a good level of discussion.


David Short

Having a beer the other night with a friend who assisted a delivery from The Netherlands to Portugal last month. This exact thing happened to them crossing the Bay of Biscay. They rounded up on a reach & regained control quickly, the seas were up a bit but the conditions were not difficult.