Quote by Erazmus
Most modern Motorhomes have a relay built into the 12V Fuse Board. When the engine is started a 12V signal cable causes this relay to energise and it parallels both the starter battery and the leisure battery. This charges both batteries while the engine is running.
A split charge relay only comes into effect when the van is either on electric hook up or has a solar panel. In either EHU or solar charging priority is given to the leisure battery. When the leisure battery is charged the split charge relay changes over to the starter battery and charges it. If the leisure battery voltage drops the split charge relay then reverts back to the leisure battery.
Not strictly speaking correct.
The traditional split charge relay is there to operate as stated in posts #2 and #3.
What you are describing is something which performs a function like
this unit when the engine is not running and the source is either ehu or solar.