Caravan & Camper Battery Charging

The size and capacity of these independent power supplies varies from person to person and family to family. Remembering that air conditioning and any product that generates heat uses a great deal of power. Plan your system around your basic needs and if air conditioners, heaters and microwaves are used it would be better to use mains power or a generator rated to the capacity of the products in question. Remember that even some of the new quiet generators may not be used in some parks and reserves.

Your typical family would need power for a few 12V lights, T.V., radio, water pump and an inverter to convert 12V DC to 240V AC to charge laptops, cameras and mobile phone batteries. In some cases there will be a 12V Compressor fridge that will need power if not fitted to the car and being powered off the car’s dual battery system.

Have a look at the diagram below of a typical caravan system running on 12V DC. All 12V products are wired to the battery and when mains power is available the charger will replenish the battery. In caravans without batteries a large 12V transformer is sometimes fitted to supply 12V DC when the caravan is plugged into 240V mains power.

The diagram does not show the 3 way fridge as these are normally wired independently.
240V mains products like the air conditioner and microwave can be used off mains power when available.

When mains power or a generator is not available, some other considerations to charge the batteries are:

• A solar charger


• Petrol powered battery charger


• The tow vehicle’s charging system

The size of your system will be determined by the time you stay in one place and your power usage. Most basic systems will have at least one 12V battery of approximately 100A/H, a 240V Charger, heavy duty charge cables from the car to the battery and possibly a 100W Bi fold solar panel to charge the caravan battery when in one place for more than a few days. Fixed panels on top of the caravan are also an option but you would require more panels to produce the power needed. Most people like to seek shade and many of these panels are fixed in one position and can’t be easily moved to follow the sun.

Our primary form of charging is from the tow vehicle and it needs to be as safe and efficient as possible to keep charge time down to a minimum.

The basic requirements of a typical caravan and camper charge system will require the following components when charging the battery from the tow vehicle. The following is a basic guide line and is not specific to any one vehicle, camper or charging system.

Camper or Caravan

• Suitable sized battery in the camper for your needs. Minimum 80 A/H (100 A/H is usually recommended) but make sure to leave room for more.


• Heavy fuse or breaker close to the camper battery 50 AMP or greater depending on cable size and system application.


• Heavy duty cables from camper battery to the hitch point. Minimum 8 B&S of both.


• (+) and (-) cable. 6 B&S recommended.


• Heavy duty Anderson plug minimum 50 AMP.

Tow Vehicle

• Suitable electronic battery isolator or solenoid under the bonnet close to the starting battery. Electronic isolators are better as they are automatic. Solenoids can be used but will require a switch or delay device to activate it. The isolation of the battery is important to protect the starting battery from being drained by the caravan accessories and to protect the wiring during engine starting as the heavy current used to start the engine will damage the caravan wiring if the starting battery is low.


• You will need spike protection if it is not incorporated into the isolator.


• A heavy duty fuse or breaker 50 AMP or greater depending on cable size and system application fitted close to the isolator. *Also see chart below.


• Heavy duty cables from the isolator to the tow bar, minimum 8 B&S mm2 (+) and (-) if possible. 6 B&S cable recommended. The chassis can be used as an earth if needed but make sure it is a good clean earth. Run a separate earth return if possible.


• Heavy duty Anderson plug minimum 50 AMP.

On both vehicles use protective sleeve on exposed wires and run cables where heat, sharp edges and road obstacles won’t damage the cables. Cable tie all loose wiring and treat all holes and lugs with a corrosion preventative coating. Plastic battery boxes and battery hold down clamps are recommended and make sure that the battery compartment has ventilation to prevent build up of gasses. Make sure to use suitable fuses on all wiring and accessories. Avoid causing sparks and do not smoke when working on batteries.

Qualified Installer

Consult a qualified installer if you are unsure of any D.I.Y. work. All 240V mains wiring should be done by a licensed contractor.

Below are two diagrammatic examples of wiring options and you can see which one suits your application to plan your charge system. Some of the diagrams show vehicles already fitted with dual batteries where it is not needed to fit an isolator. The diagrams also show 12V outlets in the rear of the tow vehicle as an option to save running 2 sets of wires. Make sure to fit fuses or breakers rated to the applicable wire and socket applications. Don’t overload circuits or use oversized fuses. Do not use Anderson plugs as junction points as it will make future maintenance difficult and also create a weak link in the circuit.

Note: These drawings are a guide only and not specific instructions. Every system needs to be designed to suit the vehicle, battery capacity and loads. Consult a qualified person if unsure of any DIY work.

Example 1

Example 2

Under the Bonnet of the Tow Vehicle

The photo below shows an actual system fitted to a 120 series Toyota Prado.

Batteries require regular maintenance and this should be done each time you get back from a trip and at least every 3 months if the caravan is not being used. Make sure to fully charge the batteries on a Smart Charger and top up fluid levels if needed. If you have items that may drain the batteries such as clocks and meters it is best to disconnect the batteries when not in use.