Our sailboat (Jeanneau 43DS) has been lithium powered for 10 months now – with a full 6 month cruising season in BC and Alaska mostly off grid (at anchor). It’s been a game changer not having to worry anymore about running out of power or shortening the life of the batteries by running them down to 20% or 10%. 

Lithium batteries are a big subject that I can’t address fully here, so definitely read up elsewhere to learn! This post is just to share our particular setup, since we’ve had a few people ask. I’m not an expert or an ABYC electrician, but I have read marine electrical books, ABYC guidelines, numerous online sites, and have marine electrical experience on previous DIY projects.

It’s not necessary to do everything we did just to get lithium batteries. My goal here was a ground-up complete modernization of our boat’s electrical system. Since this was a new-to-us boat and many of the electrical components were old, this made sense. Many owners replace only one part at a time (ex, batteries, shore charger, etc) but then you get a mish-mash of old and new systems. 

Lithium Batteries

First note that all boat lithium batteries are LiFePo4 – Lithium Iron Phosphate. This is a completely different chemistry than the lithium-ion batteries in your laptop, phone, etc and which you occasionally hear news stories of burning up. LiFePo4 is much safer because they cannot melt down in the same way and have built-in circuitry (the BMS – battery management system) preventing bad things from happening (overcharge, overdischarge, over-temperature, under-temp, etc). From here on when I say lithium or “LFP” it means LiFePo4.

Note “drop-in” lithium batteries means they “drop in” to the same space / size as lead acid batteries. It doesn’t mean you just drop them in and call it done. Lithium batteries require looking at your entire electrical system and likely changing a few things, particularly with the charging sources. 

Lithium benefits:

• Deep discharge capability (down to 0% even!) without memory effects. On flooded lead acid (FLA) batteries you typically don’t discharge much below 50%, otherwise you shorten the life of the battery. Switching to lithium effectively doubles your capacity – 300ah lithium is comparable to 500-600ah of what you had before.
• High charge efficiency – each amp of charging power you put in goes nearly 100% into stored energy. With FLA batteries you waste a lot of energy, especially near the end of the charge cycle. High charge efficiency is especially great for solar powered boats – we want all the sun’s power going into the batteries, not being wasted.
• High discharge power – you can draw a lot of amps at once (typically 80-100a on a 100ah battery). This is similar to AGM batteries. And it matters mainly for powering inverters. 
• Lightweight – lithium batteries are about half the weight of their lead equivalents. This makes installation easier (lifting 22 lbs instead of 50 lbs!) and can make a noticeable weight difference on smaller boats (displacement sensitive) or boats with lots of batteries. 
• Cycle count / usable lifetime – they last a lot longer, about 5000 cycles at 80% depth of discharge, or 2000 cycles at 100% depth of discharge. Different batteries may vary and advertise different things. I would take higher estimates with a grain of salt because some manufacturers are using best-case optimal lab conditions (perfect charge controllers, temperature, etc).
  Still, for most people 5000 cycles is longer than the lifetime of how long they’ll own the boat. Note that you probably don’t do a full cycle every day – we found after 180 days of cruising, we had only used 50 cycles. So if our batteries last merely 2000 cycles, we still have 40 years to go! For 5000 cycles, we’ll have 100 years.
  So although lithium batteries cost more than FLA, in the long-run they’re cheaper in terms of stored watt-hour. 
• No maintenance – with FLA batteries I had to top up the battery water a few times a year and occasionally do a lengthy equalization process. With sealed AGM batteries it’s much better but you still need to spend a few hours purchasing and installing replacements every 5-8 years. 

System Diagram

Battery Manufacturer

We went with KiloVault batteries, and choosing your battery brand isn’t an easy decision. There are a lot, and after a few searches on Google, you’ll start seeing LiFePo4 ads everywhere as the manufacturers target ads to you. 🙂

A few reasons we went with Kilovault:

• Good reviews in the marine community (panbo.com review plus the knowledgeable Rod Collins of MarineHowTo.com), especially towards having quality cells and well engineered internal circuitry (ex, the FETs are robust).
• On sale at a much better price than competitor’s options.

Some cons to KiloVault are that their mobile app (for checking battery status/health) is still on v1.0 and has one or two annoying bugs. And they can’t do BMS integration (what I would call intelligent networking) with your Wakespeed or Victron devices, so if you want that you’ll need to step up to the more expensive options like Victron’s lithium batteries and external BMS system. I’m not promoting Kilovault and we don’t have any deals with them – do your own research and you can do well with any of the reputable brands.

Other batteries we considered (with reason why I didn’t pick them – though don’t let that dissuade you – I know boaters happy with these brands as well):

• BattleBorn (BattleBorn 100 Ah battery on Amazon) – the leaders in the industry by some measures (keep in mind the market is RV’ers! Boaters are a tiny fraction compared to RV sales). BattleBorn spends a lot on marketing, and I was never able to figure out what makes their price premium worth it. It’s possible the higher cost is from all the money they spend on ads. 🙂
  They also have a very lenient charge protocol – absorption for 20-30 minutes per battery (90 min for a 3 battery bank) at 14.2 – 14.6. Lithium batteries usually have very specific “full” voltages (a 0.4v range is huge) and don’t like to continue being charged once they’re full – doing so shortens their lifespan.
  I read all their docs and talked to them by phone and email, and still couldn’t figure out if they actually engineered batteries that are more tolerant of over-charging, or if it’s just that they specified loose charge protocols as a sales tactic for novice users who don’t want to buy new charge controllers capable of more precise charging.
• Epoch – I’m hearing good things about this brand from boaters, but they weren’t around (or just getting started) when I was starting our upgrade.
• Dakota Lithium – their marketing seems to be geared towards small fishing boats and RV’ers, and they ship with a low amperage charger which is just a waste (a throw-away item) for a boat system. It was difficult to find detailed specs and charge protocols, and they recommend slow charging their batteries to preserve the cycle life ratings.
• Victron batteries – great but expensive, and the external BMS adds a bit of additional install complexity (although they do have the “SuperPack” option now with internal BMS).

One caution I’d say is there’s a lot of disingenuous marketing in the LiFePo4 battery market. Since these batteries are complex and most people don’t understand them very well, there’s incentive for companies to market them as simpler than they are, or just say whatever the buyer wants to hear in order to make a sale. It’s likely that some companies don’t bother to give good charge protocol recommendations because they know that may deter some buyers and will only shorten the battery’s lifecycle by 10 or 20% perhaps – the buyer won’t discover that until years from now, well beyond warranty range.

There are many cheapo brands of LifePo4 batteries on Amazon these days. All lithium batteries are made in China, but not all use the same quality cells and construction.

House Bank Sizing:

A big question is often how much house battery capacity do you need? This depends on your electrical needs, your daily power usage budget, your charging capacity (solar, alternator, generator), and your cruising style (do you sit at anchor for 5 days, or move every day?). 

For us we wanted to be able to sit at anchor for 3-5 days with no engine or generator usage, with 2-3 of those days fully cloudy (this is Alaska) with near zero solar energy input. Our boat previously had a 300 Ah AGM house bank, so I figured we’d go with 300 Ah lithium since that would nearly double our capacity in terms of usable amp-hours.

But I’m glad we added space for the 4th 100 Ah battery because it turned out there’s one more consideration – if you want to run a high powered inverter (we got a 2000w one) for high wattage AC devices like a water boiler, you may need a larger bank to handle the amp draw and voltage drop. Even though lithium batteries can deliver a lot of current, turning on our 1500w water boiler puts a ~150a load on the bank, which pulls the voltage down to about 12.25 – close to the recommended inverter low voltage cut-off for our batteries. 

In other words, if we had a smaller house bank we might hit low voltage cut-offs and get an inverter shut-down more often. This may vary with different brands of lithium batteries.

Lithium Challenge #1: Charge Controllers

There are 3 main things (from my view) that prevent people from being able to just “drop in” lithium batteries into an existing system without making other challenges. I’ll talk about how we dealt with those 3 challenges, but you should read up on them elsewhere to understand in full.

All the charge controllers that charge your batteries need to support the charge settings that your lithium batteries require. And no, an old charger with a “lithium” profile may not be enough. Some old and/or cheap devices claim to support lithium charge profiles, but may have inflexible settings that aren’t compatible with your particular batteries.

In our case our old Abso shore charger had a lithium profile but was destined for replacement (by a Victron Multiplus inverter/charger) because the Abso was quite basic and its lithium profile would continue to charge the batteries after they were full (our Kilovaults want only a 2 minute absorb).

The other big one is the alternator regulator – we had no regulator (just an internally regulated alternator) – so we got a Wakespeed regulator (the other option is a Balmar MC-618).

Subchallenge #1a): Charging a lead acid “start” battery

Part of the charge controllers challenge, meriting its own section is that most boats will keep their start battery on lead acid (AGM or FLA). Although there may be some LFP batteries now that can handle the big starting amps a diesel engine starter draws, most people keep the existing start bank for simplicity (furthermore a lithium battery has little benefit for the start bank, which is typically lightly used and never deep discharged, even running a windlass).

Many boats charge their start bank by “combining” their banks when charging. However the problem with that is with LFP + lead acid you’re now charging two different battery chemistries with one charge protocol. Some LFP batteries have pretty close charge parameters to lead acid, in which case you may be able to keep a combiner, but that wasn’t the case for us.

Long story short, we use a DC-DC charger from our house bank to start battery to independently charge the start battery using its own charging algorithm (configured in a Victron app like most of the other Victron charge controllers):

Lithium Challenge #2: Load Dumps (BMS Shutdown)

One of the more complicated (and less well understood) lithium challenges on a boat is your battery bank can suddenly shut down if the BMS detects a fault (over-charging, over-discharge, over-temp, etc). If you’re motoring at that time with your engine alternator cranking amps into the battery bank, that’s bad news for your alternator – it results in a huge voltage spike that can fry your alternator.

Fortunately there’s a simple solution for this – an alternator protection module (APM) like the Balmar APM. It absorbs the spike so that it can’t harm the alternator. Note that the APM can sort of fry itself (wear out) if it has to absorb too many of these events or for too long. It has a flashing green indicator light to show it’s working. We’ve never had a load dump event, and I expect they are quite rare.

Lithium Challenge #3: Fuses (Short Circuit Protection)

Lithium batteries have so much power they can dispatch (the “discharge rate”) that they require special short circuit protection in some cases. You might think a 400ah bank rated for 400a of continuous discharge is limited to 400a of output in a short circuit event and any 400a fuse will suffice. That’s incorrect (for multiple reasons). The batteries can and will put out more amps than their rating for a brief period of time, and that’s where the fuse’s AIC (amperage interrupting capacity) comes into play – a Class T fuse can “interrupt”, or stop, at least 20,000 amps.

I have heard of people using only MRBF fuses, which have a 10,000a AIC – that may or may not be enough, and it depends on the battery specs and battery bank size. If you’re not sure, consult a marine electrician. Or just get a Class T (yes, they’re expensive, and bulky).

• MarineHowTo.com explains this better than I can: MarineHowTo: Battery Banks and Over Current Protection

Products We Bought:

• Kilovault LFP batteries – 100ah (altestore.com) x 4 = 400 ah.
• Victron DC-DC 30a non-isolated charger – to charge the start battery (also the windlass battery) from house bank. Note Victron makes isolated and non-isolated versions of this, non-isolated is what you want for boats.
• Wakespeed alternator regulator
• Balmar APM – For BMS load dumps. Some people design alternate mitigations for this, but the device is only $60-80, easy to install, and small (doesn’t take up much room).
• Fuses:
  • Blue Sea Class T fuse holder with Class T 300a fuse
  • MRBF fuses on LFP battery positive posts – in some ways these are redundant with the Class T, but I already had several of them from the previous system, and they protect against a short within the battery bank wiring – ex, if a battery inter-connect chafed through or became disconnected, or simply if you accidentally created a dead short while working on the batteries.
• *** Items below may not be necessary for a lithium upgrade but were part of our overall upgrade: ***
• Victron SmartShunt 500a – if you don’t have a battery monitor yet, this is one of the easiest changes you can make.
• Victron SmartSolar MPPT 100/20
• Victron CerboGX
  The Cerbo is basically a communications hub, and I debated whether I really needed it. It really breaks the KISS principle we try to follow on boats, and remote monitoring and logging of our electrical system isn’t something I felt I needed (although afterwards I had to admit it’s kind of cool).
  But, to use the Victron GX display (next item) you have to have a Cerbo. That display is pretty awesome so it felt worth it.
• Victron GX Touch 50 display
  The GX display is your battery monitor but also much more – shore power usage, inverter/charger monitoring and control, and can display additional things like tank level monitors or temp monitors (if connected to your Cerbo).
  If we had decided not to do the GX, then the only other option was the older Victron displays or connecting to the SmartShunt via the Bluetooth phone app.
• Victron Multiplus 2000va inverter/charger
  I had a lot of debates between a 2000va or 3000va (which is slightly more popular). The 3000va is really big and would’ve been hard to fit. Some people’s attitude was you want more capacity than you need, but in my opinion that’s silly – when it comes to electrical inverters, you want exactly or only slightly more than what you need. Excess inverting capacity is just wasted space / money / lower inverter efficiency.
  2000va has ended up great for our needs. We can run our 1200w hot water boiler or 700w coffee maker, and we don’t need to run those things in tandem.
• Big lug crimpers (FTZ Heavy Duty Lug crimpers) – for 2/0 gauge
  

Some of the product links are Amazon affiliate links which mean we get a small kickback if you buy through Amazon. We bought much of this through Amazon for convenience (fast free shipping) and price competitiveness, but I wouldn’t necessarily recommend that on some of the bigger, more complex items (like Victron MultiPlus) if you might need technical support.

Victron doesn’t provide direct consumer support, requiring the distributor to do that, and Amazon Victron resellers sometimes don’t provide the best support. For a big ticket Victron product (like the Multiplus) I’ve had a good support experience (and reasonable prices) through BayMarineSupply, as well as for any marine electrical parts you can’t find on Amazon (ex, tinned Ancor wire and quality ring terminals and butt connectors can be hard to find there).

Summary:

After 6 months of use in full-time cruising (through BC to Alaska), lithium batteries have been a game changer for us. Even though we had a lot of rain from April thru June, we did fine with 350 watts of solar (the same level we had on Violet Hour 1, which had much lower electrical needs). This is likely due to the efficiency of lithium batteries – every amp of solar or alternator charging stores nearly that full amp of energy in the batteries, rather than losing some of it.

But the real game changer has been no longer having to worry about getting our batteries charged up fully. Lithium batteries don’t care if they’re kept between 40-60% for a few days (or a week or a month), or cycled up and down between 60-80% every day. Previously, our lead acid batteries were a constant source of minor anxiety – a resource we needed to worry about managing, like our water and diesel supply. If we had several cloudy, rainy days at anchor, I would worry about battery health because there was no way to keep them charged up on solar and we’d have to consider setting up our portable generator, which I always hate to do. 

Downsides:

There are not many downsides, but with all the other gear I added it has to be said that this makes the boat’s electrical system more complicated. Our boat is now a fairly complex computer – Victron gear is great, but there’s a lot of software running behind it. If you don’t have the time or skills to debug some software issues, then you may find the added complication a bit frustrating. 

The three things that have given us the most trouble / complication are: 

• Wakespeed alternator regulator – complicated to program, and its Windows firmware update program is buggy and temporarily bricked the device once. 
• Victron CerboGX – the “communications hub” – it has an issue where it loses its wifi connection sometimes and gets stuck, unable to connect to all working wifi networks. Solutions / Threads to reference: 
  • https://community.victronenergy.com/questions/82877/cerbo-gx-wi-fi-issue-when-having-the-gx-touch-conn.html
  • https://community.victronenergy.com/questions/131716/cerbo-wifi-and-internet-connection-reliability.html
• Victron Multiplus 2000va inverter / charger – complicated to program, and its charge configuration options are behind the times. It doesn’t support better lithium battery management options such as tail current cut-off and absorption times shorter than 1 hour. It’s still better than most of the alternative options though.