Recently bought 1st van 1990 ABI award transtar. there is a built in charger, spring connectors on the battery, also a cable with two crocodile clips tucked away in the battery compartment. there is also a 3 way switch on the main panel (car/caravan/off). when mains connected and switch to off all fine, but without mains can get adequate power when connected to car but when switched to caravan i have low power fading quickly. i have been connected to mains for a week on site and driven 700 miles connected to car. how do i configure switches/ battery connections to charge battery either from mains or car when travelling.