Caravan & Campers Guide to Battery Chargers

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:

• AC to DC charging from 240V mains power or a generator.
• DC to DC charging from the tow vehicle while driving, often with solar input as well.

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.

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1. Quick answer

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.

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2. Multi-stage charging

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:

• Bulk: the charger applies the highest safe charging current.
• Absorption: the voltage is held while current tapers down as the battery fills.
• Float: the charger maintains a fully charged lead-acid battery at a safe lower voltage.

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.

Lead-acid charging profile

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 profile

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.

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3. AC to DC battery chargers

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:

• Battery chemistry: AGM, flooded lead-acid, gel and lithium all need the correct profile.
• Charge current: match the charger output to the battery manufacturer's recommended charge rate.
• Adjustability: a selectable output can help if the battery bank is upgraded later.
• Installation position: mount close to the battery where practical and use the correct cable size.

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.

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4. DC to DC battery chargers

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.

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5. Cable size and voltage drop

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.

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6. Before choosing a charger

• Confirm the battery chemistry and charge profile required by the battery manufacturer.
• Check the recommended and maximum charge current for the battery or battery bank.
• Check whether the vehicle has a smart alternator.
• Allow for solar input if the charger will also control solar panels.
• Size the cable and fuses for the charger current and cable length.
• Keep 240V wiring and fixed mains work for a licensed electrician.

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.