Motorhomes

Two different types of battery can be found in motorhomes and marine applications. The starter batteries, which are responsible for starting the combustion engine, and the on-board batteries, which supply the lighting, refrigerator, radio or television, for example, when the engine is switched off.

Both battery systems are charged while the engine is running. Important is that the battery systems are separated from each other when the engine is switched off so that, for example, the TV does not drain the starter battery and it is then not possible to restart the combustion engine including the alternator.

The use of a starter battery is generally not recommended. Starter batteries are designed for short-term power output so that they can be recharged immediately after starting the combustion engine.

On-board batteries are designed to withstand cyclical loads. They can deliver relatively low currents over a longer period of time.

In the caravan / marine sector, lead-acid on-board batteries are almost exclusively installed, which are designed for cyclical battery use. Sufficient cycle stability, good voltage stability over a long period of time

The specification C10 or C20 is always linked to the battery capacity in Ah. Two values are often given:
e.g.: 225Ah (C10) and 242 Ah (C20)

This means that the battery can release more current if it is discharged for more than 20 hours, i.e. the faster the battery is discharged, the less current it can release.

Cycle-proof on-board batteries are available as liquid, gel or AGM batteries. The main difference between a liquid battery and the gel and AGM batteries is that the acid has either been thickened (gel battery) or, as with the AGM battery, has been absorbed by a glass fibre fleece.

In the latter two cases, this prevents acid from leaking even in a lateral position and even if the housing is damaged, no pools of acid can escape.

There is also a significant advantage: they do not emit gas and therefore have no external ventilation and are maintenance-free.

People often ask which battery type is better? There is no general answer to this question because it always depends on the application and the requirements. Both types have different strengths and weaknesses.

If you are currently using a liquid battery and are considering a conversion due to the maintenance-free, non-gassing, longer service life and higher capacity, you should first clarify whether the existing charger is also suitable for AGM or gel batteries. At the same time, you should bear in mind the operating conditions.

If you only use your on-board batteries a little, you will probably get by with the inexpensive liquid version. If, on the other hand, you plan to use your batteries more cyclically and expect a high power requirement, you will not be able to avoid a conversion in the long term.

Lead-acid on-board batteries last a very long time if they are always full as often as possible and are discharged as little as possible. The following standard errors occur again and again in practice:

The batteries are so large that the charger, wind generator or solar panels do not provide the necessary charging current to fully charge the batteries. This damages the batteries in the long term. The capacity decreases. A charger that is designed for the battery capacity provides a remedy.
The batteries are too small. The refrigerator or the daily TV programme draws so much current from the on-board batteries that a deep discharge occurs and the batteries are damaged. In this example, the battery capacity needs to be increased. Please consult us or your caravan / marine specialist before investing.

The following sample calculation can be used to roughly determine the required capacity (Ah) of your battery system:

(power 60 watts (W)) / (voltage 12 volts (V)) = amperage 5 amps (A) * duration of use / day in hours (h), e.g. 10 h = required capacity in ampere hours (Ah) 50Ah

This calculation can be used to calculate the load individually and determine the total capacity required by adding them together. As the usable capacity is not the same as the specified capacity, the calculated capacity must be multiplied by a factor depending on the battery type.

In this case, we suggest the following factors:
50Ah * liquid battery factor 1.7 = 85Ah
50Ah * factor AGM / gel battery 1.4 = 70Ah

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 is different charging technology 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! Please do not experiment!