Hi, went to fit a leisure battery to our 2012 vito dualiner and then found it already has an auxiliary 2nd battery under the drivers seat, plus a split charge relay thing that joins that batt to the alternator once engine is running. Yay. Now, I want to figure out how to do the wiring... I want the aux battery for camping situations and just need to power: 1. a couple of USB ports for phone charging 2. A 12v socket for a waeco fridge 3. A bunch of 12v LED spot lamps (ikea!) which are going in the headlining. 4. The headunit (upgraded the audio20 to an Alpine INEs900r, which I later found Merc offered as a top of the range media option from the factory, albeit with Alpine badge scrubbed out. 1-3 relatively easy - just need a small bus bar and fuse box, plus the panel thing I got off ebay which includes a voltmeter, usb ports and 12v socket. Bit I dont't know how to do yet is how to rewire the stereo so that it is powered off the spare batt, but still ordinarily goes to sleep when I key off. I.e want it to turn off when I switch off the engine and remove the key, but still possible to turn it back on from the on button on the headunit, but drawing power from the aux battery instead off the main starter battery. Any ideas?