Electric Boat Batteries: A Beginner's Guide

Electric boat batteries are the power source for electric boats. They store energy that is used to power the boat’s motor.

Several types of electric boat batteries exist, including Lead-Acid, Lithium-ion, and Nickel Metal Hydride (NiMH) Batteries.

Understanding the basics of electric boat batteries is crucial because they are such an integral part of how electric boats work. So, let’s explore the topic in detail.

🔋 Types of Electric Boat Batteries

This section briefly overviews electric boat batteries, their types, and their features.

Three battery technologies are generally used on small marine craft applications.

Lead-Acid Batteries

This is the oldest technology and is still one of the most commonly used, where relatively small current values are required. The name describes two technologies with the same chemistry but different internal constructions.

Wet Cell
AGM (Absorbed Glass Mat)

The chemistry of each design is identical, but the structure of the units is different. For this article, they are being treated as the same.

Lead Acid batteries are regularly the primary electrical power source for secondary systems in internal combustion engine cars and boats.

They are affordable and have been used for decades in various applications. However, they are heavy, have a limited lifespan, and require regular maintenance.

The one advantage that lead acid batteries have over other technologies is that they can withstand vibration, which the others cannot.

Their four main weaknesses make them less suitable for powering a boat that uses an electric motor. These are listed below.

Lead Acid batteries are only discharged to 50% of their capacity. Draining the battery below 50% causes permanent damage to the battery.

It will reduce life expectancy by significant margins.

Lead Acid batteries used with internal combustion engines primarily power the starter motor. Once the engine begins to run, it powers an alternator, replacing the charge for the starter motor.

Electric motors require continuous discharge, which Lead Acid Batteries do not cope well. Once the battery is at 50% charge, it must be considered fully discharged, or the unit’s expected lifespan will be compromised.

Lead acid batteries will not last longer than 2 – 3 years.

If they are regularly discharged to 50% and then recharged (as opposed to the trickle charging current provided by a car or boat alternator), the life expectancy will be reduced to 2 – 3 years.

Lead acid batteries are heavy and can take up a lot of space on a boat. They also require regular maintenance, including topping up the electrolyte levels and checking the terminals for corrosion.

Lithium-Ion (Li-ion) Batteries

Lithium-ion batteries are the primary technology for most current-generation electric vehicles and boats.

The reasons are as follows:

This means that Li-ion batteries can be discharged more than lead-acid batteries, typically to 15% of capacity.

For a given battery size, the user will enjoy almost twice the time between charges compared to a lead acid battery.

Li-ion batteries are becoming increasingly popular for electric boats due to their high energy density and lightweight design. They can provide more power per unit of weight than lead acid batteries,

Typically, Li-ion batteries weigh 1/5th of a similar capacity lead acid battery.

Using a lithium-ion battery will directly impact the boat’s range in a marine application where weight equals drag and, therefore, reduced performance.

If Li-ion batteries are looked after, they can be comfortably expected to last for 10 years or more.

While a Li-ion battery may cost more than a lead acid battery, the increased life expectancy generally results in a lower ownership cost over the unit’s life.

Li-ion batteries are essentially maintenance-free as there are no fluid levels to top up.

This has a follow-on advantage in that there is no acid to leak out and no corrosion on the terminals.

There are two downsides to using these batteries.

The Disadvantages Of Li-ion Batteries

But it’s not all rose-tinted glasses. The downsides of lithium-ion batteries are listed below.

Li-ion battery cost is felt at the initial purchase. Lead acid batteries cost less than ½ the price of an equivalent Lithium-ion battery.

As the life expectancy is generally more than 4 – 5 times that of a lead acid battery, the lifetime ownership cost is lower.

Li-ion batteries are easily damaged if they are placed in a vibrating environment.

This is, however, easily overcome by ensuring that they are installed in a secure location and adequate cushioning is provided.

Nickel Metal Hydride (NiMH) Batteries

NiMH batteries are becoming more common in electric boats.

They have similar benefits to lithium-ion batteries in terms of their energy density and lightweight design.

They are also less expensive than Li-ion batteries.

NiMH) Batteries require minimal maintenance. They are more environmentally friendly and are free from the transportation regulations that Li-ion batteries must follow when shipped.

The key characteristics of NiMH batteries are listed below.

NiMH Batteries Have A Longer Expected Lifespan

NiMH batteries are expected to last longer than lead acid batteries and require less maintenance. However, they do not have the life expectancy of Lithium-ion batteries.

Li-ion can last 5 – 10 years (1,000 charge/discharge cycles), whereas NiMH lasts between two to five years (500 cycles).

NiMH Batteries Are Low Maintenance Technology

As with Li-ion, NiMH batteries are maintenance-free units.

NiMH Is Out Performed by Li-ion Batteries

While both Li-ion and NiMH outperform lead acid batteries, the overall performance champion is Li-ion.

NiMH Batteries Charge Faster Then Lead Acid Batteries

While NiMH batteries charge faster than lead acid batteries, Li-ion is the winner in this category.

Li-ion batteries charge faster, perform better in extreme temperatures, and hold their charge longer than NiMH batteries.

📈 Battery Capacity and Performance

The battery capacity is an important factor when choosing an electric boat battery.

It determines how long the battery can power your boat before recharging. The capacity is measured in ampere-hours (Ah).

The higher the battery capacity, the longer the battery will last. However, a higher-capacity battery also tends to be larger and heavier, which may not be practical for all boats.

Choosing a battery with the right balance of capacity and size is important for your specific needs.

Another essential factor to consider is the battery’s performance. This includes its ability to deliver a consistent power level over time and handle high loads.

The different battery technologies should be cared for according to individual requirements.

Regular Inspection

Lead Acid Batteries should be regularly inspected as follows:

✅ Check the external appearance of the unit, looking for any discoloration that may indicate leaking fluid.
✅ Check the acid levels to ensure sufficient liquid inside each cell.
✅ Check the battery terminals, particularly looking for corrosion or other damage.

Li-ion and NiMH Batteries are generally maintenance-free. Despite this, it is always a good practice to check the general condition of the units.

Being exposed to water is dangerous and should be avoided at all costs. If the battery is exposed to water, it should be disconnected from the system and dried off immediately.

Keeping The Battery Clean

With all the battery technologies, the terminals should be kept clean and tightly connected to the terminal connectors.

If you find corrosion, disconnect the battery and remove rust with a steel brush or emery paper.

Proper Storage And Charge Maintenance

If the battery can be easily removed, it is a good practice to remove it when not in use. The battery must always be stored in a dry and well-ventilated location.

A good option is to store the battery in a home garage near an electrical plug outlet. This allows the battery to be connected to a trickle charger. This will ensure it stays fully charged.

🪫 Charging Electric Boat Batteries

All battery technologies discharge at 5-10% a month when left alone. This means they should be connected to a trickle charger when they are stored. So, let’s discuss how to charge an electric boat effectively.

Types of Chargers

While lead acid batteries can be charged using a conventional charger, NiMH and Li-ion batteries are charged differently.

Li-ion Batteries

Li-ion batteries use chargers equipped with a safety feature that monitors the charging process and cuts the power if a problem arises.

NiMH batteries are much harder to charge than Li-ion batteries because they don’t have a “float charge” voltage and must be charged using a constant current.

They are also more vulnerable to damage if they are overcharged. A charger that is rated for Li-ion and NiMH batteries must be used, respectively.

Two types of chargers can charge electric boat batteries.

Onboard Chargers

If the dock has charging facilities, then shore power can charge boat batteries effectively. The most convenient system is an onboard charger that is wired in permanently.

When the battery needs to be recharged after a day on the boat, the charger can be plugged in and charging started.

This also applies when the boat is not parked up.

When the boat is not in use, ensure it is parked near an electrical outlet and can be plugged in to start charging.

Portable Chargers

Portable chargers can be moved to the boat and plugged in as required. This makes them very versatile. The main issue is that the portable charger must always be remembered and brought along for each trip.

Sounds simple, I know, but there have been far too many instances when yours truly, acting like a true genius, left the charger at home.

You’ve heard the saying, “Happy wife – happy life.”When you have planned a weekend away with the family, this results in an unhappy wife!

We now have a rigid checklist to ensure this doesn’t happen again – it is followed religiously!

🎯 Sizing and Selection of Batteries

The following factors must be considered when selecting the optimal battery for your boat:

Batteries designed to power an electric boat must be categorized as deep cycle technology.
Electric boat systems are generally configured in 12, 24, or 36 volts, depending on the size of the motor. These outputs can be achieved by connecting a series of batteries together or by installing a dedicated unit that produces the DC power required.
The physical size of the batteries must fit into the battery box on the boat.

Because the discussion of electric boat batteries depends on the size of the boat, we have explored the topic of batteries for electric outboard motors and electric trolling motors to better inform you.

🛑 Safety and Handling of Batteries

Because batteries are widely used in all spheres of life, it is easy to become blasé when handling the unit.

Although batteries represent relatively little risk, they should be handled carefully, appropriately installed, and kept in optimal condition.

Proper Installation

The installation of the electric boat batteries must be done correctly. The battery location must have the following characteristics:

It must be watertight.
It must not be exposed to sunlight.
It should be well-ventilated (this is particularly important for Li-ion batteries, which have been known to have runaway thermal events.
All wiring must be correct, and all connections must be secure and fastened tightly.

Disposal and Recycling

The argument for renewable energy systems such as electric boats falls down somewhat when the time comes to dispose of used batteries.

If they are placed in a non-optimized facility, there is a real risk that severe fires or other polluting actions may happen.

Because of this, under no circumstances must the batteries be disposed of along with your regular garbage.

The batteries must be taken to a specialized battery recycler or retailer at the end of their useful life. These facilities will dismantle the battery and extract the Lithium, Cobalt, Nickel, and Manganese used in its construction.