[Loki9]

My P30 has two 12V batteries and the usual off->1->all->2 big red battery switch. Printed right on the switch it says "do not change when engine is running". Why is that, what's the harm? It seems to be the make-before-break type of switch, so that if I have the cabin lights on and slowly move the switch from 1 to "all" to 2 the lights never flicker.

Is it safe to switch when the engine is idling and the alternator is not working?

I'd like to use one battery for starting the engine only and the other battery for everything else. However, can I start the A4 using "1" and then switch to "2" to charge the other battery only? I assume this will charge the battery that needs it faster than using the "all" position.