How to use Lithium batteries

Lithium batteries are gaining ground every day in the nautical world. They are lighter, take less space, they also have a much longer lifespan. They are more expensive to buy but not necessarily to use depending on the program. A brief overview of your possibilities of use for your boat.

First of all, in order for you to understand better…

Some information that you should know about batteries for boats

  • Capacity or “storage capacity”
    This is the amount of power that a (new) battery in perfect shape, is capable of supplying when it is charged. It is expressed in Amps-hour (Ah) or in kWh.
    In reality, as it is not recommended to go lower than a certain percentage of discharge, you can only use part of the capacity: 40 to 50% for a lead battery, 80% for a LITHIUM.
  • The charge and discharge current of a lithium battery is expressed in amps. This capacity represents the potential current output of the battery. Its unit is amps A or C (ratio of charge or discharge current / total capacity).
    A 100 Ah battery with a C1 can supply 100 amps.
  • The rate at which a lead-acid battery discharges also has an impact on its capacity: the faster it gets discharged, the lower the actual capacity of the battery becomes. (this is not the case with a LITHIUM battery).
    This discharge rate is indicated in the form of: C10, C20, C100…
    For example, a battery of 70 Ah in C 100 will actually have a capacity of 70 Ah if it takes 100 hours to get discharged but it will drop to only 50 Ah in 10 hours.
  • Cycle life
    When we talk about a number of “”charge-discharge”” cycles, this corresponds to the number of cycles before the degradation of the battery is such that its use is no longer possible for its initial intended use.
    A cycle is equivalent to a full discharge and a full charge of a battery. A battery that is discharged at 50%, and is then recharged to 100% will have a half cycle.
  • THE DOD : Depth of charge is related to the number of cycles. This is the discharge rate taken into account to estimate the number of cycles (Often 80%) Thus, a battery that is often discharged to 100% will have a shorter lifespan. Manufacturers indicate the number of cycles that the battery can complete before losing some of its capacity.
    • The best AGM batteries can reach 500 cycles (50% DOD)
    • The best LIFEPO batteries can reach 3000 or 4000 cycles (80% DOD)

Advantages of Lithium batteries

Real capacity

Lithium batteries withstand being discharged deeply very well without altering their cells (but you should still avoid going beyond 80%). In addition, they have a very flat discharge curve which makes them usable even with a low charge. This is not the case of lead-acid batteries which on the one hand do not like deep discharges, and in addition to that, they no longer supply enough voltage for the normal operation of devices when discharged more than 50%.

At the end, a lead-acid battery of 100 Ah, can not be used under 50% of charge compared to 80% of discharge for a LITHIUM battery.

Comparison of discharge curve of a lithium-ion battery vs a lead-acid battery

Energetic efficiency

Lithium batteries have an efficiency close to 100% against 80% for a lead-acid battery. 1 Ah injected into the lithium battery will supply 1 Ah while a lead-acid battery will only supply 0.8 Ah. (This is very important when recharging with solar panels, wind turbines or hydro generation. This keeps you from losing 20% of the production as heat).

Lithium batteries are very light and less bulky (3 times lighter).

One disadvantage: its price

Lithium batteries are on average 3 times more expensive to buy than good lead-acid batteries.
But the cost can be amortized over time.

Let’s take the example of 2 AGM batteries 12 V 100 Ah and Lithium batteries and compare the specifications.

Rated Capacity100 AH100 AH
Real capacity/Maximal discharge rate50 AH80 AH1,6 fois + de capacité
Cycles à 80 % DOD5004500Durée de vie X 10
Cycles à 55% DOD80010000
Weight40 kgs13,6 kgs3 fois plus léger
Battery size329 x 179 x 278260 x 168 x 2121,8 fois moins encombrante
Prix achat 100 AH affiché3001000
Prix achat 100 AH disponible6001250
Prix d’utilisation par cycle1,20,3 4 fois moins chères sur la durée

What can you used lithium batteries for ?

In view of the comparison of the specifications, we recommend Lithium batteries for those who prefer less weight (races or light boats that can not be overloaded) or for those who want maximum capacity in a minimum of space.

They are also recommended for intensive use (life on board, long trips, electric motorization, large number of people on board) where its large number of cycles will amortize its initial cost.

Are LITHIUM batteries dangerous ?

All means of storing energy are potentially dangerous, whether it is lead-acid batteries, fuel cells, gas cylinders, or gasoline or diesel tanks. In all cases, precautions have to be taken and procedures are to be followed. You will not store a gasoline container in a room that is not ventilated and that is near a source of heat !

What is thermal runaway ?

This is the feared phenomenon in LITHIUM technology. This is a chemical reaction of the cells in the event of improper use (overload, exposure to fire, piercing, etc.). This results in a release of heat which can degenerate into a fire that is difficult to control or an explosion.

This should be put into perspective because on the one hand this phenomenon is something that could happen with all sorts of storage technologies (gasoline, fuel and even diesel), and on the other hand, it is easy to avoid if you take the proper measures to do so, particularly by using a good BMS (Battery management system).

Thermal runaway depends a lot on the technologies used.
In fact, the term “Lithium ion” batteries comprises several types of technologies whose characteristics are very different.

  • LCO : Lithium Cobalt Oxide
  • NCA : Nickel Cobalt Aluminium
  • NMC : Nickel manganèse Cobalt
  • LIFEFO ou LFP : Lithium Fer Phosphate
  • LTO : Lithium Titanate Oxyde

The term “”Lithium ion”” therefore has no precise meaning and often covers LCO, NNCA or NMC batteries contrary to LIFEPO.

LCO and NCA batteries are the most sensitive chemicals, NMCs are much less prone to this risk and LIFEPOs have almost zero risk.

Whatever the kind of chemistry used, thermal runaway cannot occur with good quality cells and a suitable BMS, which means one that is able to monitor the parameters to be controlled (cell temperature, voltage, charge and discharge current, cells and battery pack balance, etc.), communicate them to the user, and most importantly trigger the corrective measures automatically: switch off the BMS by opening the contactor or in the case of electric motorization for example, as with OCEANVOLT, reduce the consumption or the charge.

In addition to the BMS, you must take care that the producers (solar panels, chargers, hydro generators, generators, alternators, etc.) comply with the instructions given by the battery manufacturer. (same for a lead-acid battery).

Mechanical protections

In a good LITHIUM battery, the cells are enclosed in sealed coverings which are themselves enclosed in a sealed case and resistant to shocks, vibrations, piercing, etc …

In conclusion, the risks of using LITHIUM batteries made by a responsible manufacturer with proper installation done according to the rules is therefore minimal. In addition, the norms to be respected CE/RoHS, UN38.3… are very strict. Numerous laboratory tests (piercing, heat, shocks, vibration, etc.) are necessary before putting them on the market.

Popular belief


Contrary to popular belief and to lead-acid batteries, there is no risk of dangerous degassing (except under extreme temperatures) and even less risk of acid projection.

To learn more about lithium and rare earth elements, take a look at our article about Sailing: Electric motor, LITHIUM batteries and environment for boats Nautisme : Moteur électrique, batteries LITHIUM et environnement pour bateaux.

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