Most modern camper van conversions incorporate a 220v electrical circuit alongside the standard vehicle 12v circuit, often powered by an inverter run directly off the leisure battery. The 220v circuit allows you to run equipment such as fridges, heaters, water heaters and entertainment systems which can often draw much heavier current loads.
Adding a leisure battery will allow you to run lights, pumps, heaters, phone chargers, fridges and audio visual equipment without running down the vehicle battery and potentially leaving you stranded. It’s not a complicated procedure and vehicle electrics are relatively straightforward so it’s a job that should be within the grasp of most confident DIY …