Everything you need to know about boat batteries

After cold winter months, the new sailing season begins every spring! Before you set sail, however, the boat should be maintained and spruced up. Winter is therefore the right time to plan, order and install new purchases. This includes, for example, new batteries that may have lost power over time. But what are boat batteries anyway, what are the different types and which battery do you need for your own boat? All the answers are here.

Topseller in the category Boat Batteries

What types of boat batteries are there?

There are several types of boat batteries that come with different advantages and disadvantages. We present the variants to you in more detail:

  • Lead-acid wet batteries
  • Gel batteries
  • AGM batteries
  • Lithium batteries

Advantages and disadvantages of lead-acid wet batteries


Lead-acid wet batteries are considered inexpensive batteries for use on boats. The batteries are maintenance-free and can be installed without any problems, even at greater inclination. Therefore, they are particularly suitable for sailing yachts. Lead-acid wet batteries can provide continuous power as well as short and high energy output for starting.


However, they should not be stored for long periods without trickle charging. For installation, you should note that during use and charging, gases are generated and escape from a valve. Therefore, lead-acid wet batteries should always be placed in well-ventilated places and are unsuitable for narrow or poorly ventilated boxes.

Advantages and disadvantages of gel batteries


Gel batteries are similar to lead-acid wet batteries, but are treated with thickener to give them a gel form. This prevents them from leaking and makes them suitable for use anywhere on board, except overhead. The batteries have a high internal resistance, so they can be stored for a period of time without being charged.


But again, batteries should not be deeply discharged, as this can cause damage. Gel batteries are often used as service batteries for the vehicle electrical system and its consumers. They are unsuitable as an engine battery, as they are not particularly good at delivering short or high currents. Therefore, gel batteries should rather not be used as an engine battery.

Advantages and disadvantages of AGM batteries


"Absorbent Glass Matt" means that the acid is absorbed and bound in a glass fleece. AGM batteries have become popular on boats because they combine all the advantages of gel and lead-acid batteries. This is why AGM batteries can be installed in any position, are maintenance-free and shock-resistant. At the same time, they hardly discharge themselves and the charging process works very quickly. AGM batteries, unlike lead-acid or gel batteries, can be discharged deeper. In addition, the popular boat battery is ideal for use as both a starter and a consumer battery. Since AGM batteries provide continuous power up to a deep discharge of up to 50 percent, you can also use them for electric drives.


If you want to discharge AGM batteries above 50 percent as an exception, you have to expect that this will significantly shorten their service life. A discharge over 80 percent even leads to battery death.

Advantages and disadvantages of lithium batteries


The most expensive, but at the same time the best solution are the lithium batteries. Lithium batteries are not only extremely light, but also have a high energy density and have extremely high capacities. The output voltage hardly drops, if at all, even at low charge levels. At the same time, lithium batteries can be charged quickly and are especially popular in modern electric boats. You can fully charge a lithium battery in just one to two hours.


However, even these high-quality and expensive batteries can suffer damage from overvoltage or deep discharge. Therefore, battery management systems (BMS) are installed by manufacturers to protect against application errors as well as short circuits. In addition, they continuously measure the charging currents, condition and battery temperature.

Which battery for an outboard motor?

Which battery is suitable for an outboard motor always depends on the brand, size, type as well as power consumption of the electric motor. Important factors to consider when choosing a battery are:

  • Desired driving time
  • Weight of the battery
  • Ease of handling
  • Same nominal voltage of motor and battery


Batteries such as lead-acid, AGM or lithium batteries are suitable as an energy source. The latter in particular have greater power and are light and fast-charging. At the same time, they can be used in a partially charged state without any problems. With lithium batteries, there is also the possibility of recharging the battery via solar technology, making the operation of your boat even more favorable.

What characteristics must boat batteries have?

Compared to conventional batteries, boat batteries are designed to meet the changing demands of the high seas and have, for example, low self-discharge. This is especially useful during the winter months, when batteries cannot always be charged.

These are the characteristics that the battery for the boat engine should have:

Capacity: the capacity in boat batteries is measured in amp-hours and indicates the amount of electrical charge that the battery can store.

Power of the consumer(W) x operating time(h) / battery voltage(V) = capacity(Ah)

Cold start current: this value indicates the maximum current that the battery can provide for thirty seconds at a temperature as low as -18 degrees Celsius.

Reserve capacity: the reserve capacity indicates how many more minutes the battery can provide enough current without falling below the required voltage level of the boat.

How long does a boat battery last?

High quality boat batteries can last up to ten years. On average, however, you should expect them to last around three to five years.


What should be considered when caring for and using boat batteries?

When using and caring for electric motor batteries on a boat, the following things should be considered:


Boat batteries should not be charged and left on board, but better removed or at least disconnected. This will ensure that no consumer is still drawing power from the battery. When removing and disconnecting, make sure that the negative terminal is always disconnected first. It is best to remove the battery and store it in a place that is not too warm. The cellar rooms in your own home with a temperature of around ten degrees Celsius are ideal.

Charging the battery

Before you remove the battery, it should be fully charged. As a rule of thumb for the so-called "trickle charge" applies: at least every three months, batteries should be clamped to a charger and charged to 100 percent during the winter period. This ensures that the capacity is maintained. Before you go back on deck, you should also charge the marine battery to 100 percent.


Special feature for lithium batteries: Lithium batteries should have a state of charge between 20 and 40 percent and should be stored at a temperature of 5 to 15 degrees Celsius. Some lithium batteries can also be easily deactivated via the Battery Management System (BMS) if they are no longer used in winter.


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Häufig gestellte Fragen - FAQs

Was ist eine Bootsbatterie?

Die Bootsbatterie ist speziell für Boote konzipiert und unterscheidet sich deutlich von anderen Batterien: Diese kann lageunabhängig eingebaut werden kontinuierlich über einen längeren Zeitraum Strom für das Boot liefern.

Wie werden Bootsbatterien noch genannt?

Bootsbatterien werden auch „Marine Batterien" oder „Bordbatterien“ genannt.