Re: Flat Battery / Rear Demister
Most car radios have a "sense" wire connected to the ignition switch. The radio only turns off properly when it senses the ignition is off. It is in a sort of sleep mode when the engine is running.
So, at the back of your radio there will be two positive wires: one is for power and goes to the battery; one, the "sense" wire, goes to some power line that is fed via the ignition switch (very little current is drawn).
The hilarious thing about GTV V6 p2 (dunno about others) is that the bundle of wires that you push into your radio (put together in the factory), has those two positive wires going straight to the battery. The "sense" wire is permanently thinking the ignition is on.
This was the problem I had when I had a discharging battery. The radio, in its sleep mode (ignition sense "on"), draws just enough current to be too much and in a few days will drain your battery.
Not all radios are the same though. Mine was a pretty common Pioneer.
Its worth checking!
(if your radio works with the ignition switched off then you probably have a wiring job to do)