The Offshore Voyaging Reference Site

Eight Steps to Get Ready For Lithium Batteries

Many cruisers have already made the jump to lithium batteries, some with good results and some not, and I have already written about how to make that decision in a rational way while filtering out the screaming from the fanboys on one side and the naysayers on the other, so we don’t need to go there again.

But what if we have made the decision to stick with lead acid while we wait for lithium to get more reliable, easier to install and maintain, and less expensive? Pretty much always happens with comparatively new technology.

This is particularly worth thinking about since, although I’m neither a lithium fanboy nor a hater—I have come within a whisker of selecting lithium twice—there is little question in my mind that lithium will indeed become a no-brainer for most cruisers some time in the next five to ten years.

That is, if some other technology does not come along that renders lead and lithium obsolete, always a possibility, but my guess would be not a high probability one, at least not in that time frame.

So that begs the question: Can we future proof our boat electrical system for lithium?

That’s a hard no:

I have spent much of my life in high technology, and while salespeople love to babble on about how future proof their product is, that’s pretty much always rubbish.

Predicting the future direction of technology at the level of detail required to truly future proof anything is near-impossible, so best not to waste time worrying about it¹.

That said, if we are contemplating improvement to, or replacement of, a component in our lead-acid system anyway, it is worth thinking about how to do that in a way that has a probability of being lithium friendly.

Here are some ways to do just that:

¹Eric Klem started an excellent thread on just this in the comments to an earlier article.

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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—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Part 3, Current (Amps) Requirements and Optimal Voltage
  33. Lithium Battery Buyer’s Guide—Part 4, Fusing
  34. Lithium Buyer’s Guide—Budget: High End System
  35. 11 Steps To Better Lead Acid Battery Life
  36. How Hard Can We Charge Our Lead-Acid Batteries?
  37. How Lead Acid Batteries Get Wrecked and What To Do About It
  38. Equalizing Batteries, The Reality
  39. Renewable Power
  40. Wind Generators
  41. Solar Power
  42. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  43. Battery Monitors, Part 1—Which Type Is Right For You?
  44. Battery Monitors, Part 2—Recommended Unit
  45. Battery Monitors, Part 3—Calibration and Use
  46. Battery Containment—Part 1
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Rob Gill

Hi John,

In 2016, we had recently converted to a MasterVolt LiFePo4 bank, creating a new dry and cool electrical locker in a large void space under a quarter berth, removing two big and old AGMs from in front of our engine and two more from a lazarette – not the places for mounting Lithium batteries. We also replaced much of the wiring and switching.

Then I read one of your first articles on the comparison between lithium and other battery technologies. You made the excellent point that cruising off grid, one important benefit of lead acid if faced with total battery/system failure, is the ability to go ashore almost anywhere populated on the globe and buy a couple of replacement truck batteries. Not possible with lithium.

Since we cruise to the Pacific Islands and would need to await our return to NZ to fix any lithium system failure, this made me think how to replicate your lead acid redundancy. So we ran new cables back from the main buses into the engine space, isolated with electrical tape and then heat shrink. We left the tie-down mounts in place in front of the engine, the space empty, with spare truck style tie-down straps ready.

To convert back to lead acid, all we have to do is isolate our three lithium batteries using their manual isolators, and cable up the two new truck batteries. The simple original BEP battery monitor which currently monitors just our lead acid start battery, will also show the new house battery state without change.

So perhaps consider a P9 – when renewing your electrical setup, plan for the far more demanding environmental needs of lithium batteries, not lead acid.

And P10 – plan for redundancy, to revert back to lead acid if you ever need to.

Paul Clayton

Sometimes the simplest, most obvious solutions are the most ingenious!

Emile Cantin

Hi Rob,

FYI, I installed my own Lithium battery right where the old one was, which is in the engine room. I’ve been monitoring the temperature while motoring as obviously I was worried about over-heating, but the highest I’ve seen is 38°C after ~24 hours of continuous motoring (my max range anyway). From what I’ve seen, electric cars routinely heat their battery packs to ~40°C to improve performance (especially when charging), so I think this is not an issue at all.

In fact, looking at the datasheets, my old AGM didn’t give ranges but the “capacity-temperature” chart topped at 40°C, while the specs for my new Lithium say the charging can go up to 55°C and discharging to 60°C.

So yeah, I think lithiums don’t have especially onerous environmental requirements, except cold-weather charging. And even then, if it’s so cold you can’t charge, you’re probably stuck in ice.

Rob Gill

Hi Emile,

Interesting observations, thank you. The highest temperature we have observed on our batteries is 30 degrees in Fiji (also sea water temperature). Our marine electrician had us place a large vent in the forward (cabin) end of the locker to provide some air flow, and we left provision to put in a couple of computer style ducted fans if needed – but haven’t so far. He also recommended charging below 35 degrees Celsius which could equate to an internal battery temperature of 70 C. At 40 C under hard-charging you could be close to 80 C internal battery temperature, and getting close to your battery limitations?

The bigger environmental concern for me is maintaining low humidity and minimising the salt / oil vapour in the air, something that would be difficult to achieve in the engine bay, especially when you have a water leaks that are not uncommon events, like a recent SW leak we had that we eventually traced to the rear seal on our raw water pump. Or as happened recently, the cylinder head pressure relief valve blocked and we had oil spurting from the dipstick around the engine bay.

Our batteries have both an internal and external BMS with integrated electronics and ethernet style connections for communications. In the locker, we also have the battery isolators, and 2x controllers for solar panels, alternator, shore power unit and the inverter. We treat this space more like a computer server room than a battery locker, and the batteries more like microcomputers with over specified battery backup capacity!

I have two DampRid containers in the space, which I monitor and replace about once a quarter. So it is dry in this locker with no sign of corrosion anywhere after seven years.

A last consideration is we have been able to mount the batteries and electronics above the cabin floor level, just under bunk height. In a flooding event, we buy some vital time with electrical power. In our engine bay, the old AGM batteries needed to be low down at sump level, to enable engine access to things like our SW pump.

Rob Gill

Hi John,

My understanding is each MasterVolt battery (we have three) has an integrated BMS function that communicates over the MasterBus to the Masterview management and monitoring system. If the batteries lose their connectivity, they can still operate electrically, AND isolate themselves independently in a fault scenario by triggering their individual safety relay. Sorry, I don’t have a more detailed understanding to share. Spec here for the current product (ours is slightly earlier version):

Will email photo separately.

A last thought is that Maritime NZ (and Australian counterpart) are currently revising the electrical standards for vessels under 12m and over 12m in length, which will include changes to physical housing with special requirements for lithium batteries. I very much doubt that our engine bay environment would meet this new standard, without major modification, and so become non-compliant for insurance purposes. I was alerted to this by the marine electricians who installed our MV LiFePo4 system. Replacing our engine start battery recently in the engine bay with a high capacity AGM, it was installed in a new acid proof box with integral cover, to meet this new incoming standard.

Rob Gill

Thanks John,

I tend to think of the system as a distributed management system. I can monitor the batteries using the Masterview display, and by connecting a PC to the management bus with the MV app, change the set-up parameters, bring the batteries back on line if they have shut down and more.

If I connect a PC to the internet using mobile data (or say StarLink), our MV dealer or MV themselves can access the system and diagnose issues with any MV device connected to the MasterBus, especially the lithium batteries.

Philip Wilkie

Of all the articles on this topic, this one is the most pragmatic and widely applicable of the lot. I have found myself in several conversations with sailors a lot more competent than myself, but struggling a little with the complexities of this topic.

Most real world boats were built for 12v lead acid based systems, yet the hugely improved performance of lithium is undeniable. Given increasing expectations it is inevitable the upgrade/conversion question will arise. The gold plated approach which is to rip and fully replace with a new (and logically a shift to 24v system voltage) is not an accessible option for most – instead most will be served best by an incremental approach as you outline above.

Correct cable sizing and fusing is rightly the first priority. Far too many existing marine installs have been unsafely modified and extended over time that the forgiving nature of lead acid allows you to get away with. The same wiring with lithium becomes a death trap.

Fast acting Class-T fusing will feel like an overkill for many – but frankly the cost of these items is a fraction of your annual insurance bill. Most people have no idea of what happens when 20kA or more of fault current blasts through a wiring system, the physical violence is shocking. Search for “arc flash fault” videos for some diverting action.

This article is a very useful summation of a lot of other prior material published here, and I will be pointing others to it.

Andre Langevin

Class T are 20 000 A. MRBF are 10 000 A. Given the ABYC 7 inch rule, MRBF fuse should be on every positive pole of a Lithium battery. Since there exist MRBF terminal connector its feasible.

It is not in all installation that Class T fuse can be the primary fuse for each lithium battery.

Once the battery cable has been protected with the MRBF, Class T fuses can be installed on the parallel link (after the battery have been combined ) downstream. Then you are ABYC compliant.

Philip Wilkie

Yes I understand the point you are making – mounting a Class T fuse within 7 inches of at least one terminal is not always easy to physically achieve. Which begs the question of why 7 inches? If anyone knows for certain I would be interested to know.

I am guessing that this length is short enough to be unlikely to physically reach across the terminals of a typical lead acid battery. If this is the rationale then yes it makes sense to place a MRBF fuse on both the positive and negative poles. Especially as lithium batteries may well have different dimensions and the 7 inch rule might not work so well. But the problem with these relatively slow blowing fuses is they do allow for a lot of energy to pass through under a fault condition and this is what causes the damage.

Therefore you say – it then makes good sense to then place a single fast acting Class T fuse in the positive line – at the point where all the sources and sinks are combined. On my benchtop have sent a 400A Class T fuse to that big fuse-box in the sky and it was remarkable how little fuss was involved. A short crack sound and then nothing, no smoke no damage anywhere – and this was with at least 25kA of fault current available at 24v from a LTO bank with an internal resistance of under 1 milliohm!

I quite like your suggestion and I may well adopt it – it achieves the best of both worlds; useful protection of the high ampacity battery compartment cables, and high speed discrimination, low energy fault clearance to protect the far more vulnerable wiring and equipment throughout the vessel.

I would be curious to know if anyone can spot an issue with this.

Mark Young

To be clear – are we talking about a T fuse per *BATTERY* positive or per cell positive that goes to make up that battery?

I think fusing the positive of each cell is the most secure way forward, followed by a class T at the main *BATTERY* positive.

With Lithium a cell can have an internal short and cause havoc. So how do we effectively address those concerns?

Roger Gleason

why is this if it blows at 10,00? Because it doesn’t blow fast enough?

Roger Gleason

thanks, good to know, yes an article would be helpful for us electrically illiterate

Andre Langevin

Hello John,

A very good resumé. I also love the comments so far. With my experience of designing and installing energy systems on boats i could suggest:

A) Identify everything that can put a charge, solar, alternator, fuel cell, windvane, water turbine and for each of these check if the charging profile is adaptable to Lithium. Most windvane are not programmable… Many charging source not coordinated can work against each other. Clean that up while you are on Lead Acid. With Lithium it is of prime importance that you don’t create a high voltage event because a charging source went south.

B) Choose your manufacturer against the philosophy they have toward the BMS. For example Victron has a BMS with a dedicated alternator port, so that old non programmable alternator can still be used safely and contribute somewhat to the charging process – although not completely efficient.

C) In the same vein as B, insure that all compatible charge controllers have access to the voltage of the target battery correctly. It means sometime to rewire the alternator so that the S (sense terminal) is not on the starting battery.

D) Invest in solar because with Lithium its worth it. Previously with lead acid you had to charge the battery early and we all know the sun shine more at noon. Now with Lithium you are not bound to the charge/discharge that occurs when a cloud obscure the sun.

E) Install measuring shunt as several key places so that you can check where is the current going, and from where is it coming. Very important unless you are an octopus with multiples Fluke clamp on amperemeters.

F) Separate your current house banks in pair A and B that can be isolated from one another. Very useful later.

G) If you have bought a boat recently or are not so sure about the electrical system, have someone knowledgeable come aboard and inspect it, recommend conformity upgrade and draw you a high level view of your system. And why not a transition plan toward lithium in several stages if required. Worst come to worst, it could be valuable to say to a insurance underwriter in the context of a claim, that you have not improvised becoming an industry professional.

And my last comment is about the complex battery monitoring and control systems. You are totally right that the attention should not be given to that. The focus has you layed it and also from the comment of others is on safety and preparation. On all my customer installations I suggest a Cerbo and a VRM account so that I can remote monitor the customer installation and set my own set of alarms rules. The cost is less than 3 % of the total energy upgrade cost. for the people i have worked with, its invaluable visual tool in their understanding of their new system (especially the woman aboard who prefer a visual graphical interface than a bunch of numbers on dials)

My humble 2 cents

Emile Cantin

Hi John,

I recently switched to Lithium, but I wouldn’t consider my installation “finished” by any means. I wasn’t really planning on switching as I was in the middle of cruising towards the Bahamas, but I had to face the fact that my AGM house battery was shot so I looked for a replacement.

As soon as I started shopping for batteries, one thing became apparent: Lithium batteries are now only ~50% more expensive than AGMs now. So I made the switch; only for the house battery now. The charging sources I had that could be switched to lithium were connected to the lithium battery (only solar for now). The rest was connected to the start battery, and I added a DC-DC from the start battery to the house battery.

The plan is to evolve that installation and move the alternator to the lithium battery (I have a Balmar regulator) as soon as I can get one of these Sterling protection devices.

Anyway my point is this: while my lithium setup isn’t ideal, it’s still delivered lithium’s main benefit in my view, which is that it’ll happily take partial charges all the time. I no longer have to worry about my battery except looking at the percent-value on my BMV. High charging current is another benefit that I’m yet to take advantage of, but it wasn’t that important to me.

Eric Klem

Hi John,

Probably no surprise but I think your suggestions are very reasonable. This is a case of where there are a few basic things you can do from a best practices standpoint but trying to buy the exact right box that does everything is a fools errand until you put the entire system together which is the time to do it.

And to your comment above, I think an article on AIC would be great, it is definitely an important topic that seems to get very little thought. With the size of some of the battery banks these days, I think a lot of people are not protected in the way that they think as even a class T can’t handle the potential current from that big of a bank and the batteries need to be separated with multiple fuses instead of all in parallel with a single fuse.


Dick Stevenson

Hi John and all,
I looked but may have missed a comment on this: would lithium batteries on a boat need to have inside warm storage in northern below freezing locations. Would they survive just sitting for 4-6 months of below freezing temps when charging is not possible or would they need to be removed from the boat and brought inside?
Thanks, Dick Stevenson, s/v Alchemy

Olivier Le Carbonnier

I recommend reading the 4 articles on lithium batteries on this website:

Craig Buchner

Hello John, I’m a novice (to the group and Lithium knowledge level) . I have a question regarding Point #2 – separate load and charge busbars. Can you elaborate on how having separate charge and load busbars benefits a Lithium system. In the chapter on BMS, you speak of multiple relays to shut down individual charging DEVICES but I’m unsure how having these separate busbars makes a difference.