Switching To Lithium Batteries On A Boat | Become A Cruiser
Installing Lithium Batteries on a Boat

Switching to Lithium Batteries On a Boat

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A Primer – Installing Lithium Batteries on a Boat

We have had lithium batteries on our boat for four years. They have been fantastic. They cost a king’s ransom, but how they have changed energy availability on board has made them worth every cent.

Four years ago the path to installing lithium was not quite as clear as today. Lithiums were viewed as cutting edge technology, unproven, and very few marine techs even wanted to touch them.

I was fortunate that prior to buying our boat I was in the alternative energy business and a large chunk of that business dealt with lithium batteries. So I had a pretty good understanding of what the risks and challenges of converting a ten-year-old boat to lithium were.

This article is a primer for anyone considering the switch from traditional lead-acid batteries to Lithium batteries for their boat. It is not meant to be an all-encompassing how-to guide for building and installing a DIY lithium battery system on a boat.

My intention is to spark the thought process for a boat owner who is unfamiliar with lithium battery setups for marine applications. So, that boat owners can see that changing from lead-acid to Lithium batteries requires a holistic approach. Merely swapping out lead-acid batteries for lithium without considering their relationship to the rest of the boat’s electrical system is a potential recipe for disaster.

Lithium Batteries are not a Silver Bullet

I would like to start by saying that Lithium batteries are not a magic bullet to solve your boat’s electrical power problems. Batteries’ sole function is to store energy. If your boat does not have enough DC power generation be it from solar, wind, alternator, and/ or generating charging, installing lithium batteries will not solve your power charging issues.

It’s All About The BMS

A battery management system or BMS is essential for the safe long-life operation of a lithium battery system. Simply put the BMS will prevent the battery from doing anything that is likely to harm the battery (or the rest of the electrical system).

Typical BMS Protections (Cut-off) Include:

. Low cell voltage
. High cell voltage
. Maximum current flow
. Short Circuit Protection
. Cell temperature

Unlike a lead-acid battery, lithium batteries cannot self-balance the individual cells in a battery. A good BMS will also include a balancing function to bring all cells up to the same voltage when certain preset conditions are met.

A networked BMS can control some or all charging and load systems in an electrical system. A high quality networked BMS will also be able to modulate charger output to ensure that the total safe maximum output is not exceeded.

There is No Such Thing as a Drop-In Lithium Battery

Prior to tackling a conversion from lead acid-based batteries to lithium batteries on a boat. One needs to look at the whole DC electrical system. Whatever the marketing folks say there is no such thing as a drop-in lithium battery replacement for lead-acid batteries.

Drop-in replacement batteries relate to the size of the battery only. Some marketers will say that a battery that includes an integral BMS is a ‘drop-in replacement battery’.

When we speak of lithium batteries on boats we are referring to Lithium Iron Phosphate (LiFePO4). The charge voltages min and max are a function of chemistry.

All manufacturers building LiFePO4 cells which are then assembled into batteries end up with a battery that is a few decimals of a volt different for charge profile between manufacturers. These charging and float voltages are very different from traditional lead-acid batteries. And charging and maintaining a lithium battery at lead-acid voltages will guarantee a short lifespan for the lithium batteries.

If one digs into the product literature for these so-called “drop-in replacement lithium batteries” one of two things are evident.

  1. The “Drop-in Battery” manufacturer hides the correct voltage settings in the owner’s manual or installation paperwork where it is immediately evident that the batteries require the same care and protections as with any other lithium battery installed on a boat.
  2. The manufacturer has no intention of supporting any warranty claim and is in business for a quick buck before exiting the market place.

Now that we have cleared up the confusion around “drop-in replacement batteries”. Let’s take a look at what parts of the electrical system are required to be evaluated when installing lithium batteries on a boat?

Lithium Batteries on a Boat Compatibility Checklist

Electrical ComponentDetails
Charging SourcesCharge Profile – Must be programable between:
13v and 14.4v (12V system)
26v and 28.8v (24v System)

– Chargers that charge at constant current/ constant voltage are recommended. In other words, the charger will charge at a constant current up to a set voltage (+/- 1-2% from full) and then will taper the current to maintain the correct voltage to the point it shuts charging off.

– Most high-quality brands manufactured in the last 6-8 years will meet this capability

– On units with a preset lithium charge profile set by dip switches or a rotary switch, ensure that the generic setting matches or is close to the required setting laid out by your battery manufacturer.

A Preset setting +/- 0.2v of your battery chemistry may be acceptable provided Max charge and float charge are not exceeded.

Where battery charge profiles are set by dip or rotary switches make sure that the setting does not exceed any recommended charge voltage. Particularly the float voltage. Floating a lithium battery at a voltage point above where the battery is “resting” will dramatically reduce the life span of Lithium battery systems.

Charging at too high a voltage as the battery nears 100% capacity greatly increases the possibility of battery “runaway”

Where preset profiles are your only option lower charge voltages for float and bulk are always advisable to exceeding max voltages.

Lithium Batteries Maximum Charging Current
– Up to 1C (charge current = battery bank capacity i.e. 600amp battery bank could theoretically accept up to 600amp charge current).

Normally 0.5C is recommended over the life of the lithium batteries.

Check your battery spec sheet for maximum recommended charge current.

Networked Operation

Ideally, choose charging sources that can be networked together and controlled by the BMS.

This reduces complexity when building in protection systems to the system as in a networked system the Battery Management System (BMS) will be able to control all networked devices.

Where networking is not possible due to equipment from different manufacturers and vintages it may be possible to design a relay system driven by the BMS to control some or all charging sources.

This type of system does add increased complexity to the installation and introduces multiple avenues of failure for protection and normal operation.

– Solar Charge ControllersUnless your battery system is networked and has a BMS system that can manage the entire charging profile consider the implications of having batteries that will accept pretty much whatever charging current you feed them with.

Think about having full solar, wind, and alternator output flowing into your battery system across various components of your electrical charging system for many hours vs minutes for Lead-Based battery systems. See below for more details.
– Wind Generator See Solar
– AlternatorAn external alternator regulator is recommended.
We have tried 3 different external alternator regulators on our boat and the best one I have found by far is the programmable/ CanBus – network-enabled Wakespeed External Alternator Regulator.

Alternator Protection device recommended – This device will protect the alternator from a sudden shut-off triggered by the BMS in systems where the alternator charges the lithium battery bank directly.
– Battery Charger (Generator and Shore Power)Lithium batteries can absorb a much greater change current.

You may be able to shorten your generator run time by purchasing a battery charger(s) with a much higher charge current. A high-capacity Inverter charger such a the wildly popular Victron Multiplus 120Amp Charger 3kw Inverter is an excellent choice for a high capacity battery charger for lithium batteries on a boat.
Inverters– If the inverter cannot be networked to be shut down by the BMS system. The inverter will then require an alternate method for the BMS to turn off the inverter in a low voltage or battery over-temperature situation. Such as a relay control.

– Due to the higher discharge ability of lithium battery banks you may want to invest in a high output Inverter or even an inverter charger such as the hugely popular Victron Multiplus inverter/ charger which can charge up to 120amps and produce 3000 watts of clean AC power.

– With a high capacity Inverter +/- 3Kw it is entirely possible to run a high capacity AC watermaker.
Main DC Distribution Bus BarA battery protect device or smart relay programmed for lithium battery usage is required to protect the battery bank from under-voltage/ over temperature events. By shutting off current flow to the load side of the electrical system to prevent the battery voltage from falling below the minimum safe voltage.

Ideally, this smart relay/ battery protection device should be networked to be controlled by the BMS
Battery/ Engine/ House SwitchesEnsure that the switches are rated to manage the increased charging and or current draws that the lithium system will introduce (Bigger inverter loads etc.)

The greater charge acceptance of lithium batteries will mean that your battery switches/ cables/ alternator etc. will all be forced to operate at a much higher amperage than the lead-acid system the lithium replaced.

Increased electrical currents, which are sustained at a higher amperage for longer may very well exceed the design specifications of many components in the charging system.

One of the most overlooked items when switching to lithium is the design rating of ALL electrical components in the charging system.
Battery Cabling and Bus Bars Use the Bluesea Systems Circuit Wizard to verify that the battery cabling on your boat of sufficient rating to withstand greater charging/ discharged loads which your redesigned battery system will introduce.

When entering data into the calculator, pay particular attention to the number of minutes that will be sustained at the newer higher amperages.
Battery Fuses– All batteries should be fused as close to the batteries as possible (preferably within 7″ or 23cm)

– Lithium Batteries should be fused with Class-T Fuses appropriate for the cabling and expected current draw.

Remember that a fuse just too small for the load is a fire hazard. Too large and it’s ineffective. Use the circuit wizard to calculate or consult a professional marine installer.
Battery Shunts– Appropriately sized shunts for expected current loads
Battery Monitor– An accurate battery monitor is essential for monitoring lithium battery banks on boats to ensure that you maintain your bank within an acceptable voltage ranger.

I cannot recommend the Victron BMV 712 series battery monitor enough. If budget is not too much of a concern the Victron Cerbo-GX monitoring system is a fantastic product and is invaluable for monitoring a complex marine electrical system.

Marine Lithium Battery Safety (LiFePO4)

Lithium batteries are a term for an entire group of battery chemistries that are lithium-based. Their safety and performance vary widely between chemistries. When selecting batteries for a role be it a battery for a cell phone, cordless drill, car, boat, or even a Boeing 787. Designers must balance performance, with weight, reliability, service life, cost, and a whole host of other considerations.

As with all technologies when the envelope is pushed there is a greater potential risk of instability or failure. And increased care needs to be taken with each application. At the high-performance end of the lithium, battery scale is Lithium Cobolt (LICoO2) battery delivering high energy at a relatively low weight. Lithium Cobolt batteries are used in portable electronics and the Boeing 787.

At the low-performance end of the technology scale sits Lithium Titanate Oxide (Li2TiO3)batteries which are an incredibly stable lithium technology. Boasting a high charge rate and very long cycle life. Used in UPS systems and street lights. Very Expensive chemistry.

LiFePO4 a Safe Chemistry for Marine Batteries

LiFePO4 Batteries used on boats sit towards the safer side of the technology. As an example, Lithium Cobolt batteries can expect a thermal runaway at just 150C (302f) where LiFePO4 will runaway at 270C (518f). And if a LiFePO4 battery does run away the thermal heat generated is only 5.5% of that of a Lithium Cobolt Battery.

LiFePO4 Batteries are the only lithium battery able to operate in temperatures up to 65C (150f).

Safety Demonstrations of LiFePO4 Batteries

Take a look at this video of common Thunder Sky Winston LiFePO4 batteries found in many marine battery packs being put through various abuse tests.


As you can see there is a lot more to be considered when switching to lithium from lead-based batteries than the actual batteries themselves.

Cutting corners on a lithium battery installation will not only lead to premature failure of your expensive new battery bank but may very well result in making your entire charging system unsafe.

I hope you have found this brief explanation of what to think about when installing lithium batteries on a boat useful. If you have any questions or would like to leave feedback. Please leave me a comment below.


Hi, I’m Nic! Our Family of four have been out cruising since 2016. We have sailed about 15,000nm, almost halfway around the world. We sold everything, took the leap of faith, and bought a 10-year-old Lagoon 380 ex-charter catamaran. We’ve fixed every system on the boat, often more than once. Cruising has been such a wonderful, positive experience for our family that I want to share my tips to help you Become a Cruiser.

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2 thoughts on “Switching to Lithium Batteries On a Boat”

  1. Great article on Lithium. We will be switching to Lithium soon.

    I have a question about shut-off relays for high and low voltage. We will buy a REC BMS and I know they provide for relay activation. But with properly controlled chargers, is a high voltage relay necessary? Our alternator (Balmar 200 Amp) has the Balmar external regulator which accurately sets max voltage. Our only other charging source is solar with Victron controllers which also accurately control max voltage (plus, we have only 400 watts). These devices have lithium settings. Our shore power charger is a microprocessor one and I think it has lithium settings too. But it can be set for proper max voltage.

    We too love our Victron 712 battery monitor. We watch it several times/day and never let our batteries go below 65%. If we had lithium batteries, we would also never let the batteries go below safe voltage. Living aboard full time allows for this. I can see that a boat at a dock may be in danger without being watched like we do. So I’m wondering if a low voltage relay is necessary?

    We currently have a 400 amp-hour lead acid bank. We use at most 35% which is 140 amp-hours (extreme case, we normally only use 20%). Seems a 200 amp-hour lithium bank would easily handle the max 140 AH requirement with little risk of under-voltage.

    Let me know what you think and thanks for putting this together.

    1. Thanks for the feedback Russ.

      To answer your question on the high voltage shutoff. Yes, it is necessary, especially from Alternator Regulators. Many things can happen within the alternator (or external regulator itself) which could cause the Balmar External regulator to fail. A failed diode and the voltage will spike. Maybe the Balmar catches it maybe it doesn’t. An issue with an alternator voltage sensing at the regulator could cause the regulator to continue charging past the max voltage. I’ve seen this happen with two chargers that have good names in the industry (not Balmar) so it does happen.

      As for the Victron solar chargers kind of the same deal as for alternators. Exceeding max current wouldn’t be such a big deal in your case as you only have 400w of solar but with 200 Amps of alternator charging and the solar you may get close. Option 1. Not foolproof set the voltage limits for the charge controllers 0.1-0.2v below the recommended charge voltages for the batteries. Or Victron sells a ‘Non-inverting’ cable which will take the shut-off signal from the Rec BMS and have it shut down the Solar Charge Controllers. I know that the Rec-Bms does integrate with Victron but would think you would still need the non-inverting cable.

      200ah would work in your situation but you will be repeatedly pulling the batteries down to 30% which they can take but will lead to a much shorter life than say if you run them only down to 40%. Somewhere around 500 cycles less cycle life. The question then is, Isn’t 2,500 cycles already enough, why squeeze out another 500. That’s up to you.

      The biggy is a 200amp hour bank with a 200amp hour alternator and solar you will be exceeding the 0.5C charge recommend by a long way. Even with the alternator derated. Most lithium can happily take 2C for short bursts but will have their life shortened if that’s how you treat them all of the time.

      Hope this helps. keep the questions coming.

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