A split charge system lets an auxiliary battery charge from the vehicles main starting battery. The key feature is that when the vehicle is not charging the “smart relay” disconnects the 2 batteries and prevents the starter battery for being drained.
A split charge system can be used in any vehicle that is charged by running the engine. Anything from a boat to a lorry. With a modern 13 pin trailer socket or the white “caravan” socket even a caravan or other trailer towed behind a car or jeep can be charged.
The key element will be the interface between the factory fitted battery and the auxiliary battery fitted to power the extra loads. This can be a “smart relay” or “voltage sensitive relay”. They work by combing the two batteries when the vehicle is charging and disconnecting when the vehicle is stopped.