The Offshore Voyaging Reference Site

Lithium Batteries Buyer’s Guide—Part 3, Current (Amps) Requirements and Optimal Voltage

Wow, figuring out how to put a lithium battery-based system together that will be functional for an offshore boat (not a camper van) and not break the bank, is even more complicated than I thought when I started this.

The good news is that we are getting a handle on it. So far we have covered:

  1. Why the BMS must be able to communicate with charging sources.
  2. Why we need a good monitoring system down to the cell level so we can properly manage charging.

Wait, it gets better. I’m confident that I can end this series with a reasonably simple checklist of buying criteria, although we will have to wade through at least two more in-depth chapters first, so I can link each checklist item to an explanation.

We need real understanding, not:

  1. Cruiser looks at YouTube.
  2. Cruiser installs unseamanlike system.
  3. Cruiser maybe gets by, but knows it could have been better.

And the best news is that, at least as far as I can see at this point, doing it right won’t cost much more than doing it half-assed. Cost is about the DIY, or not, decision and/or bank size, more than the do it right or do it half-assed decision—analysis coming soon.

With all that out of the way, let’s dig into how much peak current (amps) we need our system to be able to supply. Oh, no one ever mentions that on YouTube?…Exactly…

The Amps We Need

First, let’s cover the minimum current capability that any BMS should have for us to consider it.

We all know that lithium batteries can supply huge amounts of current, and accept prodigious charging rates—think a Tesla with amazing acceleration that can be recharged in less than an hour—but that does not mean that the BMSs and batteries we will be considering can do that.

In fact, many (perhaps most) boat lithium battery-based systems can actually supply less peak current (amps) than a good1 lead-acid battery.

What gives?

It’s all about the Battery Management System we choose and how robust the internal wiring of the battery is. Let’s deal with the BMS first.

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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. 11 Steps To Better Lead Acid Battery Life
  35. How Hard Can We Charge Our Lead-Acid Batteries?
  36. How Lead Acid Batteries Get Wrecked and What To Do About It
  37. Equalizing Batteries, The Reality
  38. Renewable Power
  39. Wind Generators
  40. Solar Power
  41. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  42. Battery Monitors, Part 1—Which Type Is Right For You?
  43. Battery Monitors, Part 2—Recommended Unit
  44. Battery Monitors, Part 3—Calibration and Use
  45. Battery Containment—Part 1
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Emile Cantin

Hi John,

Maybe I missed something, but I don’t understand your position on 48v. Why would we end up with 3 voltages? If I was installing a 48v bank, I would only have a 48v bus and a 12v bus; I would not have 24v anywhere on the boat. Why would you complicate things with 24v in this situation?

Matt Marsh

In a 48 V system, you would run the main bus and all the high-power loads at 48 V. You would step down from 48 V to 12 V using a DC/DC power supply, or a DC/DC charger hooked up to a small AGM or gel cell, near the point where each 12 V load is connected.

This only works if you can buy all the equipment you need with 48 V motors and circuitry. If you want a 48 V main bus, but have your heart set on a particular fridge and watermaker that are 24 V, and electronics are of course all 12 V…. now you’re building a 3-bus system, and making a mess, and need to go home and rethink your life.

For the moment, a 48 V main bus on most boats under about 70 feet only makes sense if you have electric motors for main propulsion or if you are running air conditioning from battery power. That may change in a few years as more of the car/truck industry adopts a 48 V architecture and compatible parts (eg. refrigeration compressors & controllers) become more common.

Conor Smith

I just completed an install of a 48v “storage bank” that charges the 12v house bank through a DC to DC. Since the boat came from the factory with 12v house bank, everything is already installed and wired to 12v (so no complicated 24v decisions). If the system completely shuts down (unlikely because it is Victron) then the owner is back to where they started with the same lead house bank and 12v alternators.

The DC to DC is made by sterling energy, 12 to 48 bi-directional, so while motoring, it charges the 48 from the 12 and then when engines shut off, it back feeds to keep lead acid house bank topped off.

What is amazing is that the 48v can charge from the generator at about 7kw, (110-140 amps at 56v).

In my view, it is the best system I have installed yet. It inherently takes care of having lead backup and I think the two Cerbo monitors is really easy and intuitive.

Conor Smith

Spoiler Alert: I chose a 48V bank, and not because I was wowed at a bar! See above.

Tim Ketteridge

Conor, I think you have hit on the biggest advantage of going 48V, if you have one of the newer 48V alternators you can charge at ~100A ( 400A@12V equivalent), that along with the small wire size and bi-directional DC-DC makes this a great option.

Whitall Stokes

Here is the American Power Systems output chart for their HPI series at 12, 24, & 48v. Balmar also makes 48v alternators. You can see how engine run time would drop and generators could be obviated.

This increased power generation combined with lithium’s massive improvement in charge acceptance opens up feasible use of 110v appliances for cooking, washers, watermakers, Starlink, etc. For many coastal cruisers, you could keep the batteries charged just by motoring in and out of the harbors.

Yes, 48v appliances are rare and in most cases don’t exist yet. Yes, 24v gets you much of the way there but most still need 12v anyway (starters, NMEA2000, electronics) so you will need 2 voltages. New converters say they are 95% efficient, so that loss does not overcome the clear charge capacities and efficiencies of 48v.

Finally, I believe the RV and automotive worlds will shift to 48v. The marine world will follow. I don’t know when but I see it as inevitable.

MasterVolt has a new converter, the MacPlus 48/12-50. This way, all the DC loads can just stay at 12v while an AGM can absorb the induction loads and basically stay in float.

George L

We have gone through this quite a bit over the last 3 years and have come to the same conclusion except that we end up doing quite a bit with 230 V as well (see other comment). 24V is there now. I think 48V will be there in the future, but I won’t wait/anticipate

Stein Varjord

Hi Mal,
2900 us dollars / 2600 euros seems like an insane price for an electric motor for a high pressure pump. I’ve come across similar pricing style on other items sometimes, and it has always been a local distributor with some kind of issue. Dessalator is a French brand. Perhaps they can give a better answer or give the local representative a solid kick in the rear? You could also check price levels in other markets. Or perhaps not just the motor. A complete generic high pressure pump including the motor should be in the region of 400 euros retail. I haven’t checked recently, but it seems very likely that you can find some better deals.

Stein Varjord

Hi Mal,
400 Euros was my guess, yes, but as mentioned that’s not based on recent research. My point is that what Dessalator sells is mostly generic parts they have from external sources, like you found out about the filters.

I have no experience with the company, but they were the first or among the first on the watermaker market, so perhaps they feel they can capitalise on that?

An experience from about 5 years ago: I was insulating the boat and wanted a specific type of foam, Armacell EA B1. It’s made in Germany, which is the neighbour of the Netherlands, where I’m located. Both are members of the EU, so we have common market, no tax difference.

Still the prices in the NL were about 5 times higher, from all NL sources I found. 5 times! I bought it from Germany, of course. This type of differences are quite normal, albeit rarely such a huge difference. It’s worth looking around.

In the case of Dessalator, I’d not look for lower prices on branded parts, but try to find alternative brands that fit the system. How much that can be done depends on the physical design of the watermaker, of course. Some watermakers are totally modular and all parts can be replaced by anything else that does a similar job.

Denis Foster

Nice article, more balanced than some LifePo fan boys videos.

About inverters and capacitors, is it better to turn off completely the inverter when the 230V loads are not needed or leave it in standby ? Our natural inclination was to turn them off most of the time and on when they are needed. Is the on off multiple cycles during a day doing harm to the inverters?

Matt Marsh

Inverters don’t like being switched off while under heavy load. Turn off the AC loads first, and then turn off the DC to the inverter, and you’re unlikely to ever have an issue.

Evan Effa

I just completed switching my house bank from 6 x 110A/h Firefly (660Ah) batteries to 2 x 460A/h (920 Ah) Epoch LiFePO4 batteries. (These batteries are Victron Canbus compatible & actually show total capacity of 960 Ah. )

I won’t get into too many specifics but I had to work hard to ensure that the LFP & LA systems could not be inadvertently placed in parallel and it was quite clear that despite the high current capabilities of the Epoch batteries, all high current motor supplies needed to be serviced by lead acid batteries.

3 Fireflies were redeployed to form an accessory stern thruster bank and 3 went to be the new main engine start bank. These are all now charged together via a battery isolator along with the forward AGM bow thruster / windlass AGM.

The alternator & a single 40 Amp AC charger charges the lead acid group directly and the house bank gets charged by 2 x 30 Amp Orion DC-DC converters. (This is in addition to 3 dedicated AC house bank chargers totaling 180A +/- ~40A solar.)

So far it is working very well but keeping the 2 battery systems separate took a lot more work and thought than I anticipated.

Yes. It is a real pain working with all that 2/0 & 4/0 cable but most of it was already in place & on board. The advantages of going to 24VDC were not really very compelling for our application.

Evan Effa

Hi John,

The vessel is a powerboat (Nordic Tug 37) with a 120A Alternator controlled by a Balmar external regulator.

I do have a 9+KW generator on board so charging capacity could be as high as 240A +/- any solar contribution (550W) while underway and with the generator running. (The batteries are rated for 230A of continuous charging each for maximum 460A with 2 batteries in parallel.)

I chose to keep the alternator feeding the LA bank directly under the relatively clumsy Balmar settings and to charge the LFP via Victron DC-DC chargers; as, I could have better control, via bluetooth, over the charging settings with the DC-DC chargers. In addition, the alternator would be protected from any rare but potentially damaging BMS disconnect. I appreciate that the this does not exploit my alternator’s capacity to the maximum but like many things represents a conservative compromise. A Zeus or Wakespeed controller might be a worthy upgrade but for now, I think this can work safely.

So far, I am finding that the new LFP bank readily accepts the full charge capacity with a Bulk / Absorption voltage of 13.9 VDC and “Float” values in the 13.35-13.40 VDC range. (This float value while on shore power is really set to allow house loads to be serviced whilst keeping the LFP bank in a ~ 95% SOC range. The cell balancing appears to be more than adequate at these settings and there is virtually no risk of overcharging the LFP.)

I have not yet installed a Cerbo GX but can do so in the future if I feel that the LFP bank would be better served by the BMS controlling the charging. I am not convinced that this is needed though as I am finding that with the BT Victron smart shunt and BT access to the BMS status, I have enough information to manually oversee the charging. Compared to Lead Acid charging, I am finding the charge settings for the LFP are rather simple and straightforward with all the Victron chargers using the same 13.9V/13.35V settings.

On shore power, I can let the two Victron IP22 chargers do their thing with the Magnum 120A inverter/charger in a standby mode. When off the grid, I always start the generator manually, maxing out the chargers and monitoring the SOC manually electing to discontinue charging when a reasonable SOC is achieved.

The excellent charge acceptance is really very satisfying to see.


Conor Smith

I also recently installed a system with Epoch batteries but am less than satisfied.

The tech support is pretty good, someone almost always picks up the phone right away!

But the brochure and manuals are lacking. I do this for a living and the manual did not easily explain how to connect the Victron Cerbo to the batteries.

But once you call tech support, they walked me through it, and all was good. Appears the BMS works through CAN Bus and with DVCC on, appears to control charging sources correctly. Maybe called me paranoid, but I dont know if I would trust the batteries controlling a Wakespeed through the DVCC. In this instance, spec’d a DC to DC for now.

Most annoyingly, when charging the batteries, there is a high voltage alarm that goes off (even though the system is within voltage range). The company said they are working on a firmware fix for this issue. In the meantime, my customer can not fully charge their batteries (which will affect balancing in long-term if we can not resolve this) in the meantime.

The companies response:
“Hello Conor,
We are aware of the high voltage alarm issues and are working now on the fix. We can provide you with a battery firmware update soon that should resolve the issue. As soon as it’s available we will let you know.

I think Panbo has produced videos on youtube about the same issue I experienced.

Evan Effa

That’s interesting. I have not yet had any high voltage alarms with my system but I am charging with rather conservative parameters (13.9 V bulk / absorption 13.35 float) with mostly Victron chargers and a Magnum 120A charger in CC/CV mode.

I have not gone the Cerbo DVCC route (yet) as I wasn’t convinced it was worth the expense & now… maybe trouble?

Conor Smith

Why are the values set so low? Did you set them low because of the alarms or because you are trying to maximize cell life by holding the voltage low?

Evan Effa

After experimenting a bit, it’s quite clear that higher charging voltages do not increase the rate of charge acceptance so there is no advantage to higher Bulk/absorption voltages. And yes, in the interest of protecting the cells, I do not want or need to get to an absolute 100% SOC. 900 Ah of storage is more than enough for our needs.

Peter Carrie

Hi John,

Many thanks for the ongoing education! Great information as always! I’d make the point that voltage drop under load may have unforeseen consequences! Component specifications don’t always tell the whole story.

Last year I replaced my defunct AGM bank with 4 Kilovault 120Ah Li batteries with internal BMS. Connections are 4/0. They are each rated for 100A maximum draw, so 400 A in total max draw. I was surprised to find that my Victron Multiplus inverter (set to <12.0V cutoff per Kilovault spec) trips out when I turn on the microwave! With the existing firmware, my Multiplus doesn’t have a “temporary low voltage” setting to deal with short duration voltage drop.

I’m still experimenting with settings, but will likely need to set the inverter low voltage cutoff at a point lower than recommended for the batteries in order to avoid inverter nuisance shutdowns. But then I will potentially be bumping up against the battery internal BMS, which cuts off (per the battery spec) at 10-11.5V.

Were I to start afresh, I’d be taking your advice to use an external BMS – and perhaps going with “Victron everything” to ensure compatibility.

I may find a setting that works. Or not. Getting components to play well together is sometimes an iterative process, despite published specifications that “should” work on paper!

Peter Carrie

Hi John,

Thanks for your thoughts on this.

I’m in Canada getting a new hip and my boat’s on the dry in Florida this winter, so I don’t have access to test alternative approaches at present.

More details: The inverter is a Multiplus 3kW with 120A charger. It has a peak/surge capacity of 6kW. The microwave is a big honker installed by the a previous owner, complete with convection oven (I’ve never tried the latter feature but it’s a high power microwave, so say it draws ~1200W on “microwave only”).

The inverter is doing its low voltage shutdown @ 12V as noted above. KiloVault tech support says not to go below that, so I haven’t tried lower inverter LVD settings yet.

The inverter is located inches from the battery bank and all connections are new and tight so I don’t think there’s any appreciable voltage drop in the cabling.

Now for the punchline: According to this morning’s always-infallible internet search, microwave ovens have a substantial inrush current of 2-3x rated capacity! Who knew? So to start the beast up, it’d want about 550A (@ 3x inrush) – well in excess of the battery banks max 400A draw. I can see why the battery voltage plummets below the inverter’s LVD!

Possible solutions:

1. Your suggestion of an AGM buffer battery might work, but I’m not clear on how one would isolate the battery chemistries on the load side. I have an existing DC/DC converter that I’m using for my AGM starter battery, so could use that to charge the buffer battery in parallel.

2. Just go ahead and invest in more KiloVault batteries to provide the needed surge capacity and maintain consistent battery chemistry on the main house bank. (But, based purely on personal speculation, I think the KiloVault batteries are perhaps being phased out. Several of the dealers are out of stock on most sizes, with a “get them while you can” riff for the in-stock size.)

3. The most bullet-proof option for the long term would likely be to fit a Victron BMS & batteries and relegate the existing KiloVaults to “deep backup”.

Then again, I could always get a smaller microwave and forego my dream of baking bread with the convection oven… Choices, choices…

Thanks as always! Your thoughts have stimulated a better analysis. Hope you get out for a Spring sail soon!

Evan Effa

We have a 1200W microwave that, when running off the inverter, draws ~ 100A from the house bank. I recently stress tested our new Epoch LFP bank by running the HW heater and the microwave off the Magnum inverter at the same time (total draw 230 Amps). It showed some voltage drop from 13.2 VDC to 12.65 VDC but that’s as low as it goes. Your LFP bank should tolerate the draw of a microwave without a problematic voltage drop. I suspect there may be an issue with your cabling or some other fault creating this problem?

Peter Carrie

Thanks for your thoughts Evan. Your battery bank has over two times my capacity. I don’t know which Epoch batteries you have. Their 300Ah battery has 400A surge capacity for 3 seconds, so if you have 3 of those your surge capacity would be 1200A! So you wouldn’t have any issues with inrush current when starting your microwave. I think my problem is that I didn’t compare surge capacities between the old AGM bank and the new LFP bank. I think John’s article above made reference to “stupid” decisions, and I’m feeling kinda “who, me?” in that regard!

Evan Effa

Sorry… To clarify: Our house bank is comprised of 2 x Epoch 460 Ah 12VDC in parallel.

Peter Carrie

No worries! I should have read your comments above more closely. In that case, your 1 second battery surge capacity is a whopping 2600 A!!! You could start up pretty much anything with that! Hope you have good fuses!

William Murdoch

If the surge occurs when the alternating current voltage is crossing zero, can a capacitor add any current to the inrush?

Peter Carrie

Hi John,

Here’s an alternative thought for you: Instead of using a lead acid buffer, I could repurpose my Kilovault LFP batteries as a secondary bank, and install a Victron Lynx BMS with LFP for my main bank. If the load disconnects from the main bank for whatever reason, then the BMS triggers a latching relay to bring the backup bank online within a few milliseconds.

Normal operation would have a 1/OFF/2 manual switch to select banks and a DC/DC charger to isolate. That would allow exercising of the backup from time to time, and I could save some weight and make use of my sunk cost for the drop-ins.

Ignoring my specific case, what do you think of using comparatively ‘cheap’ drop-in LFPs instead of LA buffer batteries to provide redundancy and protect against load dumps. They’d be independent of the external BMS, and the inverter would be tripped off by the BMS and offline when using the backup (so sidestepping the inrush current issue).

Also, my 250A alternator & Wakespeed would be protected by the BMS. I currently have an add-on spike protector for the alternator but that’s likely a one-time-only protection.

Peter Carrie
Peter Carrie

Update: I checked the KiloVault specs for peak discharge current, and the 100Ah batteries have a 3-sec peak discharge current of 350 A each (100 A is the continuous rating), so 1400 A peak for my battery bank. The inverter shouldn’t be tripping off due to low voltage/microwave inrush current, period.

I’m inclined to agree with John’s and Evan’s first guess, that there’s unknown resistance somewhere. I will pull out the multimeter when I next get to the boat. Thanks Gents.

Hugo Janse

A good way to check for resistance is to feel all the connections under load >100amps. If there is any resistance it will heat up real quick. As a boat electrician I almost always find a bad connection somewhere in a system. These can be very dangerous with the high loads most boats are pulling with big inverters and other electrical goodies. I’ve seen molten heathshrink on cables and heatcoloured stainless bolts due to the heat generated from a high resistance connection.

George L

helpful series of articles,thanks.

second your recommendations concerning voltages, at least on a new installation. Almost everything is available now in 24V – lights, appliances, winches, windlasses, etc. with the exception of

  • some electronics,
  • engine starter/alternator which is about 2K more per engine in 24V vs. good old 12V

We keep the engine circuits completely separate and supply the electronics with a small 24/12 transformer. Due to the cost of wiring, it is actually cheaper to go to 24V for the rest. Ended up with lead-acid for starter, bow thruster and windlass for the reasons you wrote.

We also run quite a bit of 230V AC kit; which is also what the generators supply.

George L

Well, it would have been 4K extra, which I didn’t feel like spending. We only use them to charge the starter batteries. They are inefficient PoS, but I don’t think it matters for that purpose.

The generation of the house electricity is on separate units off the PTO, and these are highly efficient permanent magnet units that are derated (as are the engines). So I think we aren’t that far apart.

Richard Ritchie

John, I may have misunderstood the paragraph attached below but in the context I would have thought you would be looking for a higher margin of error, thus in this case increasing available capacity, rather than “down rating” to less….
Quote: All that said, when designing a system, I always want a margin of error, so I would downrate at least 25%, in this case to 300 and 150 amps respectively; still adequate for most boats, but with caveats we will discuss in a minute. Unquote
Please delete if I have missed the point….

Matt Marsh

What John wrote is just another way of stating the safety factor (or “factor of ignorance” as I sometimes prefer to call it).

The battery manufacturer states on their spec sheet that this product is rated for 400 A discharge and 200 A charge. I would therefore specify everything I’m hooking up to it to stay below 300 A discharge and 150 A charge.

As with most things in the electrical world, the failure probability and the expected lifespan for power electronics and batteries are highly nonlinear functions of actual working load relative to the nameplate ratings. Once you get through the infant mortality / factory defect period, a device that is run continuously at 50% of its rated capacity might have a mean time to failure (MTTF) of 30 years. At 90% of capacity, MTTF might be 20 years. At 100% of capacity, 10 years. At 110% of capacity, it might be 1 year.

Stressing electronic systems right to the limit is only worthwhile if you are severely weight constrained and have a high budget for testing, eg. in an orbital launch rocket. Where longevity is desired, it’s always best to err on the side of caution.

Richard Ritchie

Thanks John!
That is now clear!!!!
You can delete the tread.

Great article. And thanks for raising contactors vs. FETs. I had missed the FET failure mode issue…. The best is latching contactors…

Hans Karreman

Hi John
Again a great article, unfortunately for me it looks like the move to “lithium” wouldn’t make much sense for us, as much as I’d like to switch over.
We have a 24v sailboat with 24/12 converters for the electronics.
At present, she has 6X165ah Victron AGM’s and one 100AH AGM start battery. The AGM’s are getting up in age >10 years on a boat that has been lightly used connected to shore power while at dock/winterstorage.
The potential problem is the heavy electrical startup currents you’ve mentioned.
The 24v housebank supplies everything, which includes the Bowthruster, Lewmar Commander Hydraulic power pack that powers the winches, jib and genoa hyd. furlers.
The idea of Lithium is attractive for many reasons but weight is certainly a major plus, adding separate AGM’s for startup currents would pretty much negate the weight savings and create an overly complicated setup.
Have mis read the articles or is my interpretation of what you written correct.
Thanks for the help/advise.


Devon Rutz-Coveney

Hi John,
I have written to you guys years ago on this topic and I’m heartened to see the effort and time you are all spending on this remarkable battery technology topic. We commissioned a DIY system onboard in March 2016. We have 722 pack cycles on the system (as measured by our Orion Jr BMS). We have lived onboard now for 35 years!! Time flies….
Our system is 12volt.
We imported the cells from China directly (
The information to put our system together came from RC at Compass Marine, Eric Bretscher at Nordkyn Design, Cam Murray at Trans Marine Pro and Andrew Ewert (The Orion BMS).
It has been a ‘game-changer’ experience for us energy wise. The Lifeline AGMs were ‘bleeding us dry’. Not to mention the environmental waste involved with being forced to buy new every 3-4 years. This was hugely expensive.
The investment in LFP has more than paid for itself.
We run everything through the LFP/Orion Jr BMS system: windlass, refrigeration, starter motor (for Perkins 4-108), hot water heaterT…. We have adopted the Nordkyn ‘Parallel’ concept: a smaller 100ah AGM battery is cabled in parallel with our LFP system. In the event that the BMS opens the Gigavac contractors in our system, the boat systems will continue to function a short time while we sort out the reason for the interruption.
I read what you have stated re inverter loads (we use a Victron 3000watt), windlass loads, charging sources etc… We have not experienced any issues what-so-ever with these larger loads interrupting/tripping the BMS.
Eric Bretscher goes into a lot of detail on his website about ‘theory’ and ‘application’….. he is to be commended for this effort. Like I stated years ago, it is an easy decision to convert to LFP. One must understand the technology and then invest in quality components to support the cells.
We run the system throughout the day on the flat part of the charge/discharge curve: 13.1 volts. As loads and charge sources (solar, hydro, wind) play out during the day it is easy to see the effect and our remote system display (we have programmed PIDs into the Torque App that display the parameters we want to observe. The App is loaded onto a small Tablet computer that is velcroed to a spot at our chart table). The MAIN point is to avoid the ‘knees’ on the C/D curve: voltages below 12.8 and above 13.4. These cells will happily run thousands of cycles, ten’s of years if kept in the flat spot of the C/D curve….in our experience! This matches what RC of Compass Marine wrote many years ago.
We run our pack at 20%-80% SOC day in, day out. Our 400 ah pack has the equivalent ‘usable’ amp hours of a 900 ah lead acid pack. It weighs a fraction of what our Lifeline AGMs did.
On a personal aside: I do NOT like the Lifeline people. I once called them on the phone to query what I could be doing differently to get better performance. The person I spoke with was VERY disparaging. He said that as a yachtie, I fundamentally lacked the knowledge to use their batteries! I’m NOT kidding!
The biggest issue with LFP we have witnessed with other adopters is they have a ‘programmed’ Lead Acid mindset: they feel the need to keep the LFP ‘topped up’ …. this is really a disability when it comes to LFP. I have lots of our install photos if anyone is interested.

Stein Varjord

Hi Devon,
Great to hear from someone who has walked the walk, for years. Our system isn’t finished, (will any system ever be?), but I’ve paid attention to the same sources you mention for a decade and my work is with electric boats, where some are lithium, so your words make sense.

I don’t feel comfortable with putting lead acid in line with lithium, as they don’t match, so we have programmable DC to DC chargers to the LA start batteries, (catamaran). However, I might be wrong. A system with an external BMS and proper contactors, with no automatic fake “balancing”, should work fine that way. Then the LA battery will work as a consumable, similar to a fuse. It won’t be treated ideally, but will still last for years. It’s relatively cheap anyway. I see how that can be justified.

The lead acid mindset you mention, desperately trying to top up the bank, = destroying it many years too early, is so true! I’ve tried endlessly to explain to boaters why that’s very bad. Most get what I say, as “an interesting theory”, but seem to not be able to change their convictions. Good for battery vendors…

Our system is 24 Volt. Very happy with the transition. Made the change gradually, before we got lithium. Windlass and some more needed change anyway. Several items were already dual voltage. Almost all our loads are now 24V. My intention is to have only 24V. The navigation electronics are still on a Whisper Power converter. Not ideal. We need at least a new 24V autopilot. We do have an inverter, a modern Victron, but it’s almost never in use, as any inverter dependent system is ridiculously wasteful, if all losses are counted. The reason for going 24V is also efficiency, not copper/weight savings.

We use predominantly the same cables as we had with 12V. That means voltage drop and power loss has seemingly disappeared. I can’t quantify how much power that saves, but it’s significant. Our solar is also far more capable on 24V. The regulators can provide 50 Amp, no matter what Voltage, so 24V means potentially twice the power. We have also increased the area. Cats are easy that way.

Devon Rutz-Coveney

Thank you Stein for the response. Yes… I have heard similar reservations from others about mixing battery chemistries. The arrangement has worked really well for us for 8 years. Eric Bretscher of Nordkyn design is the person I learned about this from and he does a good job explaining the concept on his website (at the time I read it many years ago). The Parallel battery we have is seperately switched and fused in order to fend off any unexpected surprises. So far we have not had any. You will be really pleasantly surprised at how well LFP manages. It does not ‘blink’ (NO significant voltage drop) at heavy loads. With your 24 volt system I imagine the reduced amps will augment that observation. I’m not sure I understand what you mean when you write ‘efficiency’? If I was designing a system from scratch I would perhaps entertain the idea, but our system (like yours by sound of it) was a conversion from LA to LFP and everything was already 12VDC.

Stein Varjord

Hi Devon,
I’ve also read plenty of explanations, including Eric Bretchers, supporting your layout with an LA battery in parallel. It still doesn’t quite make me comfortable, but as mentioned I might be wrong, or too nitpicky.

What I mean with improved efficiency from going to 24v is that when Amps get halved, the same wire has half the resistance, or if it was close to its limit, much more. Our 12 v anchor windlass was 1 kW. The 24v one is the exact same and uses the same cables, from the house bank. They’re 3 m (10 feet) apart. The old one definitely suffered from some voltage drop in the cables and some sag in the LA batteries. Now there’s close to nothing of that and the windlass seems way more powerful.

I haven’t changed our alternators to 24v yet, but certainly will. I expect at least similar benefits from that transition. I’m really happy with the decision to change from 12v to 24v, but I wanted to completely rebuild the system and replace several core units anyway, so the cost and work difference was minimal. To me it was a no brainer. On a well functioning 12v boat, that won’t be the same.

On that note, total rebuild of the electric system, I did look into going all CanBus. It has several benefits, apart from the bling effect. Especially a greatly simplified wiring system. However, I didn’t like several other issues, especially parasitic power draw of the electronics, so I went traditional. Happy with that too.

Stein Varjord

Hi John,
Our conversion from a 12v LA system to 24v lithium was in several steps.
1. Gather knowledge and make a plan.
2. Collect parts.
3. Start implementing some of the new layout while leaving all 12v. A lot of the items like fridge, freezer, solar regulators, LED lights and more are dual voltage.
4. When step 3 has made enough change, change the house bank to 24V and feed the whole system from a 24 to 12V converter. Don’t run any big loads.
5. Move circuits one by one from the 12V panel to the 24V panel. This stage will probably never be complete, as some circuits just need 12v.

This method keeps the boat operational all but a few minutes while switching the house bank. Also the gradual progress gives plenty of time to ponder and make totally certain that everything is done right. I know a fair bit about electric systems, but I loved the pondering time I got from the slow transition.

Devon Rutz-Coveney

Thanks John, The reason I called Lifeline was for exactly the support that you mention: ‘what was I not doing right to get such poor performance?’ To be rebuked as someone not capable of understanding how to use the batteries because I was a ‘yachtie’ is just not what anyone on a boat wants to hear.
It also just shows how one person having a bad day at work or just an idiot can ruin an otherwise good brand. Oh well…. I still won’t recommend Lifeline AGMs as I still don’t know what the problem was…..
This all said, life on boats is an evolutionary process.
All the stuff that I have been through onboard (as I am sure you can relate to) have brought me to where I am now with it. As I have mentioned in previous posts: ‘nothing better than living onboard!’ For me I enjoy the “process”……You guys are a part of that with the wonderful support you provide for so many. Bravo!

The parallel LA battery (an AGM) has not been an issue onboard for us. Any battery system installed can introduce safety risks if not executed properly. I have not read Eric’s section on the Parallel LA idea in awhile either. He may have edited it by now. At the time he even suggested a way that the Parallel system could be executed that could eliminate the need for a BMS!!

Devon Rutz-Coveney

Thanks for that John.
AGM’s, I believe are a Lead Acid variant. The battery I write of that is in Parallel with our LFP pack is a an AGM. When I write LA and AGM and I am describing the same thing. Sorry for the confusion. I should have been more clear. ,
The LA (lead acid) ‘family’ I am writing of as ‘LA’ include ‘flooded’ LA (liquid electrolyte), ‘AGM’ (absorbed glass matt) and lastly, ‘Gel’.
Again…I’m not an expert, I read a lot. If I have mistaken any of this, I apologise.
And yes you are correct about equalisation of the AGM’s periodically. I did later discover from another cruiser that I mentioned this particular vendor to (after we had switched to LFP), that one is expected to equalise Lifelines’ AGMs. Just like you wrote….
This ‘dovetails’ with what I have written about any battery technology posing a potential safety hazard if not executed properly. What I mean is equalisation of a ‘sealed’ cell battery is a dubious, time intensive, potentially unsafe process. The fellow cruiser that I mention above, told me one had to do this monthly. Where am I supposed to be doing this: out at anchor in some lovely spot?? On a cruising boat the place/resources simply do not exist to routinely do this. Nor the discipline to monthly babysit the bank for hours at a time while the explosive, toxic hydrogen gases vent…..
I did try it once…. no thank you! Not a pleasant experience and certainly NOT something I am prepared to do monthly!!
Well done you that you managed so well with this. But, IMHO, not a good investment of limited funds for the average cruiser.

In 9 years of pain with these Lifeline AGM batteries we spent $10,500.00. The 3rd bank was deteriorating with poorer & poorer performance. We were on the verge of another $3500.00 spend for a 4th bank…… $14,000.00 in just 9 years! I look back at the entire experience and see myself as stupid, a glutton for punishment, or both!
It was time to find an alternative… enter Rod Collin’s excellent online tutorial. 8 years now using the information available from RC has saved us another $3500.00-$7,000.00+ on AGMs : the additional money we would have had to spend on the Lifeline AGMs had we continued with them these past 8 years. The entire LFP project cost us approx $6500.00 start to finish including shipping. The project was NOT simply changing batteries. It involved an entire electrical system refit: Fuses, Contactors, Cabling, Buss Bars, BMS, Alternator Voltage regulators…. and a long list of other stuff… $6500.00!!
These figures are in New Zealand dollars.
At the time we were taking a ‘chance’. We had never bought and imported anything direct from China. It was a totally different battery technology. One cannot project themselves into the future to know if it was going to all turn out well.

As it is now, the LFP pack will ‘see us out’: at our current usage/pack cycles, we should not need to replace them.
We owe the Lifeline AGM people a big thank you for pushing us to look for a better alternative!!
Kind of funny when one thinks about it!! Again: for you and all the others who have managed so well with their Lifeline AGM experience…BRAVO!!!

Stein Varjord

Hi Devon,
About equalising LA batteries, on our boat it’s was very easy:
1. Open the Victron Connect app on my phone or iPad.
2. Choose the solar controller or the shore power charger.
3. Under Settings, choose Equalization.
4. Nothing more needed. No need to watch. Battery compartment already has ventilation with a thermostat fan to the outside of the boat.

I agree that some lead acid batteries are far from as safe as many see them. Notably the flooded type. While charging, these give off extremely explosive gas. Some years ago I was about 50 meters away when a very large bank of such cells exploded. I fell on my ass, probably mostly from surprise, but it was LOUD. Luckily it was an open boat and nobody being too close. One guy was dunked in the water, to rinse off the acid, and then taken to the hospital. He was fine, apart from the shock and beeping ears for a few days.

However, with LA battery types and charging regimes normal on modern cruising boats, this type of event is rare, as well as far less violent. Getting sprayed in acid is not nice, but rinse off quickly and only your clothes will notice. They get holes. AGMs contain very little free fluid, and only let out gas in unusual cases, so they would be far safer.

I absolutely think flooded 2 Volt cells, golf cart type, are better than AGM, far cheaper and far longer life, but they’re absolutely not for the install and forget type of person, as they need attention regularly. Water should be checked/refilled weekly and equalisation must be done at the right time. AGM and lithium are far easier.

I think the conclusions are rather clear to most here. Things are moving towards lithium and perhaps other chemistries that have many great advantages. At the moment, they also have significant disadvantages. Some boaters are definitely better off with some type of LA battery than with lithium. Some the opposite.

The two groups will merge sometime in the future. The market operators pretend that has already happened, and try to push us towards solutions that make them more money, which is not LA solutions… Lithium is awesome, but the sellers are not our friends.

To anyone wondering about making the leap: Read loads before you pull the trigger. You MUST be knowledgeable enough to advise yourself reasonably well. If not, you’re gambling. That’s not an exaggeration.

Stein Varjord

Hi John,
What I meant with “better” was specified, and not a sweeping conclusion: Much cheaper and much more durable. I also mentioned that it will fit for few cruisers, and I recommended a lot of critical awareness before going for lithium.

The battery bank was indeed very big and for propulsion on a professionally run boat. Still a completely open boat, like a classic lifeboat. Just 10 meters (33 feet) and typically 25 passengers. No ferry but runs consecutive tourist rounds on the canals. 1, sometimes 2 hours continuous trips, with 15 mins from end until next departure, usually 7 to 14 hours per day. It had been run like this almost every day for a bit over a year.

10 identical brand new boats were delivered on the same day the year before, 2015. The 9 others preemptively got a new bank about 4 years later, meaning 5 years super heavy duty life. (The cells get 100% recycled and the company gets a significant amount of money for them). Many sometimes careless skippers means they get pushed quite low. Often to 30% SoC and sometimes 10%. No other LA battery type can get this durability. The closest, but still not quite there, would be gel cells, but at a way higher cost and some other issues. Everything in the install was top notch heavy duty and meticulously maintained. Way beyond the attention any private boat battery gets.

When the explosion happened, the battery box was lifted off, all the cells completely exposed to the outside air. It was a sunny day with no wind. The two big Mastervolt chargers (2x60Amp@48V, equivalent to 480Amp@12V) had been disconnected a bit over 10 minutes earlier, (means gassing was still ongoing, but at a low rate). A routine system inspection was being done by an electrical engineer. He had done an IR camera inspection to look for hot areas. All good. He was the guy closest, who was taken to hospital. He stood on the pier next to the boat, about 3 meters (10 feet) away, having a break (non smoker).

What triggered the explosion remains unsolved. Must have been a spark very close, but what made it? Electronics inspection hadn’t been done yet, but nothing was wrong with that after the explosion. It was all researched by the insurance company, even though the damage was fairly minimal cost wise. Just about 10 cells had blown. They really wanted to know… My guess is some tool left on top of the cells that rolled onto two poles when the boat moved. Stupid but realistic. Nothing such was found, no “weld” marks anywhere and the EE was certain he hadn’t done that, but I still think he had.

The only points of telling this story is to make people aware of a possible risk, and that it isn’t as relevant as some lithium prophets say. Not as dangerous either. If nobody was damaged by this, it means it’s not that dangerous. It’s still real, if a flooded lead acid battery is chosen. I’ve had this type of batteries on most of my boats, including the previous bank on our present cat. Before AGM, most boats did. Still many do. They’re smaller and weaker than in this story, but the points are valid. It’s general battery knowledge that it’s nice to have so one can know more about why the battery in our own boat was chosen as it was.

Devon Rutz-Coveney

Almost forgot! Sorry! 48volts, 24 volts, 12 volts…. I am not an expert but the only advantages of higher voltages are less amps, smaller cables. The ‘step down’ conversion of 48 to 12 volts sounds great. IMHO all this manoeuvring adds complexity to a system that simply does not need it,…. after using the 12VDC LFP for 8 years. Just saying…..

Andrew Reddon

First, thanks for this series. I built a DIY lithium bank in my last boat by closely following all advice from Rod Collins, Stan Honey, and Eric Bretscher, in links you provided years ago. The articles you have written since then are wonderfully clear and supplement what I used to think were the last words on the subject. I am now completely sold on the reasoning for LA backup and the solution you propose; however, there is one minor detail that I am wondering about. With the lithium system (BMS, CAN bus, alternator field current, etc.) all dark, how do you foresee getting a Wakespeed regulator and the CAN controlled alternator up and running in emergency mode for “get me home” charging of the backup bank? I am considering a dumb, single voltage, regulator set to acceptance voltage that can be switched into the field circuit and 100% manual control of charging, but that seems very suboptimal. Even if the Wakespeed were wired in somehow, I am not sure about reprogramming it for charging the backup bank at sea. I feel like i might be missing something simple.

Evan Effa

I understand the sophisticated appeal of the CAN control / Wakespeed option but a simpler solution might be just to use a dumb external alternator regulator set to service the house bank / windlass thruster LA banks and charge the LFP house bank indirectly with DC-DC chargers.

For backup for the instruments, autopilot, house loads etc., one can have a DC-DC converter in place powered from the LA banks to the DC panel with the voltage set to something less than LFP working voltages (eg 12.5 VDC).

That way, in the event of a BMS failure, you still have the alternator protected and charging to the LA bank is maintained with instantaneous backup power for the essential DC loads.

Evan Effa

OK John. Fair enough; but a Wakespeed regulator with harness is ~$1100- CAD whereas 2 x Orion XS 50A DC-DC chargers run about the same. So from a cost perspective it’s a wash.

A 30 Amp DC-DC converter / charger to provide the DC panel backup power runs around $300-. Pretty cheap insurance IMO.

(I am seeing that charging LFP is much simpler than it was with the LA house bank. I can throw a continuous 200A of charge at the 960 Ah LFP bank and do not see the voltage get to 13.9 VDC until we are close to 95% SOC. The Wakespeed advantages seem less compelling when achieving a voltage of 13.9 VDC with LFP is indicative of an adequate SOC. LA charging is much more dynamic with higher voltages and diminishing charge acceptance rates making the Wakespeed shunt-regulated charging more compelling… )

Are sailboats with their relatively small diesels routinely running alternators bigger than 100-120A? If so, the metrics might be quite different.

(A backup alternator onboard makes perfect sense in either scenario.)


Evan Effa

I agree that one wants the chargers to utilize shunt derived SOC data. I don’t wish to be argumentative; but, the Victron Orion XS 50A DC-DC charger can Network with Bluetooth and use the BMV Voltage & SOC values to regulate charging. So there are a number of ways to skin this cat and still provide safety and redundancy in case of a BMV shutdown.

Evan Effa

Mea Culpa,

I feel sheepish but thought that I would confess to changing my mind as to thinking that using DC/DC chargers to charge the LFP house bank was a good idea..

You were right John.

We have been out on our boat for week now and I am feeling a little irritated to not be exploiting more of our alternator’s capacity while underway. 60Amps doesn’t cut it when there is a 360 Ah deficit in the morning and 3 hours of running time doesn’t replenish the house bank. (To add to the angst, I thought we had a 120 Amp alternator but just looked to confirm that and see that it’s actually a 160A alternator on a good robust serpentine belt system.)

So, I am indeed wasting a lot of capacity. Adding more DC/DC chargers does not make sense. (The currently installed DC/DC chargers can be repurposed to charge the Start and Thruster banks…)

Now to explore the best external regulator for our application… (The existing Balmar MC-612 is not able to do CC/CV charging or respond to input from the BMV shunt.)

I am leaning towards the Arco Zeus (vs the Wakespeed) as I would very much like to monitor the alternator performance and adjust parameters via Bluetooth or some other continuous real-time connectivity. Arco Zeus does now claim Victron compatibility but I’m not sure to what extent…

More homework to do but clearly, utilizing the alternator’s superior capacity makes a lot of sense.

Evan Effa


It’s not the end of the world; but the current setup is more like ‘good enough but could be better’…

I will do my homework before making any further changes.

Andrew Reddon

John: Sorry, but I posted the above comment in the wrong chapter … My comment plus your and Evan’s replies should be under Chapter 28 “Building A Seamanlike ….” where you recommend a LA backup bank.