Lithium Batteries: Features and Use in Boats

See the Marinekauppa lithium battery selection

What is Lithium LiFePO4?

There are many types of lithium cells such as LiPo, LiMn, LiCoO2, LiNiMnCoO2, LiFePO4, and LiFeYPO4, to name just a few. Lithium batteries have long been part of everyday life in mobile phones, tablets, cars, bicycles and more. It is important not to confuse these technologies, since each type has different characteristics, maintenance requirements and intended uses.

LiFePO4, also known as lithium iron phosphate, lithium-ion iron phosphate or simply LFP, is a lithium battery technology well-suited as a replacement for lead-acid, AGM and gel batteries in marine environments. These batteries, equipped with a built-in BMS (Battery Management System), have a longer lifespan compared to other lithium chemistries and lead-acid batteries. They are extremely safe, require minimal maintenance, offer high charging efficiency, excellent discharge performance and are highly cost-effective over time.

A LiFePO4 battery is built from 3.2 V cells. To achieve a 12 V battery, four cells are connected in series to create 12.8 V. For a 24 V battery, eight cells are connected (25.6 V). Since the cells are connected in series (positive to negative), only the voltage increases, not the current (amperage). To assemble a 12 V 100 Ah battery, four 3.2 V 100 Ah cells are placed in series. These cells are then managed by a single BMS that handles safety, balancing and other important functions.

Advantages of Lithium

A lithium battery typically weighs about six times less than a gel battery of the same capacity.
Lithium has much higher energy density. A lithium battery can utilize nearly 100% of its capacity, whereas a lead-acid battery can use only around 25%, and an AGM battery around 75%. For example, from a 100 Ah lithium battery you can use the full 100 Ah. A 100 Ah lead-acid battery provides only about 50 Ah before it begins to deteriorate and sulfate.
Lithium batteries have a much longer lifespan — about 5–6 times longer than lead-acid.
Lithium batteries charge significantly faster. A 100 Ah lithium battery rated at C1 can tolerate a 100 A charger.
Very low self-discharge: a lithium battery loses about 80% of its charge over 8–9 months, while a lead-acid battery may lose the same amount in only 3–4 months depending on temperature.
No hydrogen gas is emitted during charging, making it safe to install in the same compartment as other electrical equipment.
Can be installed in any orientation, as there are no acids that could leak.

Disadvantages of Lithium

The biggest disadvantage is that lithium batteries cannot be charged below freezing. A standard lithium battery can be charged down to 0°C. Below this, the BMS disconnects the cells to prevent damage.
Incorrect handling or installation can destroy the battery.
Some engine alternators cannot charge lithium batteries and may overheat or become damaged, potentially causing fire. This is solved by installing a DC/DC charger.
Higher purchase price, but lower long-term cost due to the high number of discharge cycles compared to lead-acid or AGM batteries.

What is a BMS?

A BMS (Battery Management System) is the brain and safety system of the battery. It manages charging and discharging and protects the battery. The BMS ensures that all cells remain balanced and do not face over-voltage above 14.6 V or under-voltage below 10 V (for a 12 V battery). If any unsafe condition occurs, the BMS disconnects the battery from the load.

A lithium battery without a built-in BMS must be connected to an external BMS. These systems are mainly used for custom-built battery setups. For a simple and reliable solution, choose a lithium battery with a built-in BMS.

Important Considerations

Lithium batteries require a lithium-specific charging profile. Check whether your charger needs to be upgraded.
Lithium batteries cannot be charged in freezing temperatures unless they have built-in heating.
Lithium batteries allow full use of their capacity compared to only 25% from lead-acid batteries.
Many installations require one or more smart DC/DC chargers to prevent engine alternator overheating.
Follow the manufacturer’s instructions for winter storage — some batteries must be stored at room temperature and around 50% charge.
Some lithium batteries cannot be connected in series or parallel; always check compatibility.
Fast charging is one of lithium’s major benefits due to low internal resistance. A general rule is to select a charger with about 50% of the battery's Ah rating.
- Example: A 100 Ah battery → 50 A charger recommended.

Charging Lithium Batteries

Lithium batteries are lightweight, long-lasting and highly energy-dense, but fast charging is one of their strongest advantages. Because of their low internal resistance, they accept charge rapidly.

The capacity for charging and discharging is measured on the C-scale (0.1–1 C):

0.1 C = 10% of the Ah capacity
1 C = 100% of the Ah capacity

Example:
A 100 Ah battery marked 1C can be charged with up to 100 A. The same battery marked 0.2C should be charged with 20 A.

Some manufacturers require a CCCV charger (Constant Current / Constant Voltage). This means the charger supplies a constant current during charging and finishes with constant voltage and decreasing current.

Example charging times:

A 100 Ah AGM battery charged with a recommended 15 A charger takes about 6–7 hours.
A comparable lithium battery with 1C charging can be full in 1–2 hours.

See battery chargers

Engine Alternator & DC/DC Charging

"To DC/DC or not to DC/DC?" is a common question.

For safety, we recommend installing one or more DC/DC chargers (depending on alternator size) in lithium battery installations.

Why is this necessary?

Lithium batteries can accept high charging currents, which can cause the alternator to run at full output constantly. At low engine RPM, the alternator’s cooling is insufficient, leading to overheating.

Some suppliers claim that a built-in regulator providing 14.4 V output is enough. We disagree — for safety, use DC/DC chargers or Smart Battery Protect + Argofet to ensure proper control.

Simple Explanation

Engine speed determines alternator speed.
Lithium batteries have very low internal resistance and pull maximum current.
The alternator’s regulator may not reduce output because the battery does not provide the expected resistance.
The alternator overheats.

A DC/DC charger provides the necessary resistance and regulates charging, preventing overheating.

Water Bucket Analogy

Bucket #1 = Alternator
Bucket #2 = Lithium battery
Water = Current
Hose with holes = BMS alone
Hose = DC/DC charger

DC/DC = controlled, safe, reliable charging.

Discharging Lithium Batteries

Some lithium batteries are meant only as service batteries and should not be used as starter batteries. Discharge capability is shown by the C-rating, which indicates how much current can be safely delivered for short periods.

Temperature Considerations

Lithium batteries are ideal for marine use during warm months. They do not tolerate cold well. For cold conditions, choose models with built-in heating.

Winter Storage

Lithium batteries should generally not be stored in the cold. Store them indoors at 15–25°C. Some models can handle storage down to -20°C.

See battery boxes

Voltage, Amps and Amp-Hours

Voltage (V): The electrical potential the battery provides.
Amperes (A): The amount of current the battery can supply momentarily.
Amp-hours (Ah): The total capacity the battery can deliver over one hour.

Frequently Asked Questions (FAQ)

Q: Can I charge a lithium battery with a regular charger?
A: No. Lithium batteries require chargers that support lithium charging profiles.

Q: Can I use a lithium battery in all temperatures?
A: No. Lithium batteries cannot be charged below 0°C unless they have built-in heating.

Q: Are lithium batteries safe?
A: Yes. Lithium batteries with a built-in BMS are very safe and include protections against overcharge, overheating and short-circuiting.

Q: Can I use a lithium battery as a starter battery?
A: It depends on the model. Always check with the manufacturer.

Q: How long does a lithium battery last?
A: Typically 5–10 years, depending on usage and care. Most lithium batteries last 2000–5000 cycles.

Q: Can I connect lithium batteries in series or parallel?
A: Yes, if they are designed for it and the BMS systems are compatible.

Q: What is the best way to store a lithium battery for winter?
A: Store at around 50% charge and preferably at room temperature.

Q: Can I replace my old lead-acid batteries with lithium?
A: Yes, but ensure chargers and other system components are compatible.

Q: What is the efficiency of a lithium battery?
A: Lithium batteries achieve up to 95% efficiency, compared to around 85% for lead-acid.

Lithium batteries: features and use in boats