Batteries for boats

The capacity of a supply battery should be carefully matched to the energy requirements on board. Batteries last longest when they are regularly fully charged and only discharged a little. Common errors in dimensioning are

• Too large: The charger, solar panel or wind generator does not supply enough power to fully charge the battery. This reduces the capacity over time.
• Too small: Consumers draw more current from the battery than it can supply, resulting in a Deep discharge and permanent damage.

A rough calculation of the required capacity (Ah) is made as follows:
Power (W) ÷ voltage (V) = amperage (A)
Amperage × duration of use per day = required capacity (Ah)
Example: 60 W ÷ 12 V = 5 A
5 A × 10 hours = 50 Ah

This calculation can be used to determine the consumption of each individual device and the required total capacity can be determined by adding the results. As the actual usable capacity differs from the specified capacity, the calculated value must be adjusted with an appropriate factor depending on the battery type.

• Liquid batteries: Factor 1.7 à 85 Ah
• AGM/gel batteries: Factor 1.4 à 70 Ah

Converting to gel or AGM batteries can be worthwhile, especially for boats and motorhomes with higher energy requirements. Both battery types are maintenance-free, non-gassing and offer a longer service life and higher cycle stability than classic liquid batteries.

However, before you convert, you should check whether your charger is suitable for AGM or gel batteries. A liquid battery may be sufficient for occasional journeys. However, for intensive use and higher loads from electrical consumers, a conversion is advisable in the long term.

The values C10 and C20 indicate the capacity of the battery in ampere hours (Ah) and refer to the discharge time.

For example, a specification of 225 Ah (C10) and 242 Ah (C20) means that the battery can release more energy over a period of 20 hours than over 10 hours. The faster a battery is discharged, the lower its actual available capacity.

There are two main types of battery on boats and in motorhomes. Starter batteries are specially designed to start the boat engine. They supply high currents for a short time and are then recharged directly by the engine.

Supply batteries, on the other hand, provide power for electrical devices such as navigation systems, lighting, refrigerators or entertainment electronics on board. These batteries are designed to deliver consistent amounts of energy over a long period of time.

It is important to separate the two battery types so that the supply batteries do not discharge the starter batteries and thus prevent the engine from restarting.

While travelling, the on-board batteries are charged by the engine's alternator. However, an optimum full charge is usually only achieved using a charger with a 220 V connection. For this reason, every opportunity for charging should be utilised. Wind generators and solar panels are usually only used for supplementary charging, i.e. a charger is required to optimally charge the batteries and thus maximise their service life. We will be happy to help you select a suitable charger.

Be careful with the different batteries! There are different charging techniques for acid, gel, AGM and lithium batteries. An incorrect charger can damage the battery and, in the worst case, can lead to an explosion. Always seek advice!

Car batteries are suitable if the battery is only to be used to start the engine. We do not recommend the use of car batteries, i.e. starter batteries, to supply the electrical consumers of boats or motorhomes. Starter batteries are designed to supply high currents for starting the engine in a short time, while supply batteries are designed for cyclical loads. They can supply a constant amount of current over a longer period of time without being damaged. Starter batteries would wear out prematurely if used in this way.

The supply batteries with AGM technology impress with their versatility and are the ideal choice in combination with an inverter.

Gel batteries are one of the most popular solutions for supplying power to electrical consumers in the caravan/marine sector. They are characterised by their easy transportability and can easily withstand longer storage periods.

Lithium iron phosphate batteries are becoming increasingly popular, particularly due to their low weight in combination with a high Energy density. Although the purchase costs are higher, these are offset in the long term by their impressive longevity and outstanding cycle stability.

Let us advise you!