In order to determine your power supply needs, you first need to think about how much electricity you consume when you’re on the road. If you’re heading out on day trips to tackle bumpy tracks and don’t need to power anything more than a few aftermarket lights and an air compressor, then your vehicle’s stock single starter battery will probably suffice. If, however, you’re heading out on a multi-day journey with an onboard fridge, vehicle-mounted camp lights, a tablet device and sat-phone, you’ll be glad to have an additional supply.
For most car-campers, a simple 12-volt dual battery system will provide enough energy to keep your gizmos going if they’re stationary for a couple of days. In their simplest form, dual battery systems combine a vehicle’s stock battery with an auxiliary battery, which is used to power accessories. It’s also possible to link up more than one extra battery if you need extra power. Unlike a starter battery, which is used to give short sharp bursts to your motor, the auxiliary will be a deep-cycle battery, which has a slower discharge over a long period of time.
There are several different kinds of deep cycle battery that can be fitted for auxiliary purposes, including gel, Absorbent Glass Mat (AGM), lead crystal and lithium. Each have their own advantages and disadvantages, but price, weight and size tend to dictate most people’s decisions.
It’s a good idea to include an isolator switch, so your starter battery can be disconnected from the system when you’re not on the move and won’t be depleted when you’re posted up at a bush camp out in the sticks. It’s possible to install a manual switch, but it’s much easier – and more common – to include a voltage sensing relay that does the job for you.
To be of any use, your auxiliary battery will need to be charged. This is usually handled by your vehicle’s alternator, the same system that charges the starter battery when your car is running, or from an external supply such as a solar panel. If you’re linking up to the alternator, it’s wise to add a DC-DC converter to the system, which will act like a multi-stage charger, sometimes upping the voltage to provide an optimum charge rate to the battery.
If you want to charge your battery when the engine is not running, then solar panels are a great option; you can also use a generator or even plug into mains power. For any of these, the set-up will need additional regulators to control the inward flow, and possibly additional relays to prevent overcharging.
Adding an inverter to your system will give you access to a 240-volt AC current, just like the mains power at home. This enables you to charge laptops and other domestic electronics. It’s important to note that mucking about with 240-volt power is risky business, so if you’re looking to install a system that requires continuous 240-volt power it needs to be done by a licensed automotive electrician.