A battery charger is not just a way to put power back into a caravan battery. It needs to suit the battery chemistry, battery size, cable run, alternator type and the way the van is used.
Most caravan and camper setups use two charging paths:
For AGM and lithium systems, the important first check is whether the charger has the correct charging profile for the battery. A charger that is suitable for a lead-acid battery is not automatically suitable for lithium.
If the caravan has a deep-cycle battery, solar and vehicle charging, choose the charger around the battery first, then the power source. Confirm the battery chemistry, recommended charge current, maximum charge current and whether the battery management system has any special requirements.
For a simple AGM setup, a quality multi-stage AC charger may be enough. For touring, especially with a smart alternator or lithium battery, a DC to DC charger is normally the safer and more predictable charging path from the vehicle.
If you are still deciding between AGM and lithium batteries, see our lithium vs AGM battery guide before buying the charger.
Modern battery chargers use staged charging so the battery receives a high current when it is low, then a controlled voltage as it approaches full charge. The names vary by brand, but the common lead-acid stages are:
Lithium batteries usually use a different profile. They generally do not need the same long float stage as an AGM or flooded lead-acid battery, and many lithium batteries rely on the battery management system to protect the cells. That is why a lithium-compatible charger matters.
A lead-acid battery is usually happiest when it is regularly brought back to full charge. Leaving it partly discharged for long periods can shorten its life.
Lithium charging is commonly described as constant current followed by constant voltage. Once the battery is charged, the process stops or reduces depending on the charger and battery management system.
AC to DC chargers run from 240V mains power or a generator and charge the house battery from that supply. They range from small portable units through to larger permanently mounted chargers for caravan and RV battery banks.
When choosing an AC charger, check these items in order:
As an example, Enerdrive commonly recommends an AC charger output around 30-40% of the battery capacity on its Lithium B-TEC battery range. A 125Ah battery may therefore be better matched to a 40A charger than a much larger unit. A charger that is too large can be harder on the battery if it cannot be adjusted to suit.
A DC to DC charger takes power from the vehicle side and charges the auxiliary or caravan battery at the correct voltage. This is important because long cable runs, voltage drop and smart alternators can stop a simple direct-charge setup from fully charging the house battery.
Choose the output current around the battery bank size and the vehicle wiring. Some DC to DC chargers allow the output current to be reduced for smaller batteries or longer cable runs.
Many caravan DC to DC chargers also include solar input. If that matters for your setup, check whether the charger has a basic solar regulator or an MPPT solar controller, and whether it can use alternator and solar input at the same time.
Battery chargers need to see the right voltage at the battery. If the cable is too small or the run is too long, voltage drop can reduce charge performance or make the charger behave unpredictably.
This is especially noticeable when the charger is mounted in the caravan but the supply comes from the tow vehicle battery at the front of the car. The longer the run, the more important heavy duty cable and correct fusing become.
The team at Enerdrive tested three 10m cable lengths with a 40A DC to DC charger. The smaller under-capacity cable almost halved the charger output, which is a useful reminder that charger size and cable size need to be chosen together.
This guide is general information only. The installer is responsible for checking the battery, charger and wiring requirements for the specific system. If you are unsure about cable size, fusing, 240V work or lithium compatibility, use a qualified installer.
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