So, i have been having this issue as the use of my car has gone down, and i suspect it's my HU. It used to happen in my mini if 4-5 days went by that i didn't drive the motor and the only relation between my A3 and my mini is the Head unit. I'm thinking that it might just be an Earth problem as i use the Earthing that is wired into the harness and not an actual body earthing so before i go and buy myself a new HU i wanted to know: Is this a common problem, and is it caused by a faulty earth? If not is there a reason that a HU would drain the battery when the ignition is off? is there anyway to test if it is draining voltage when the ignition is off? The HU is wired to the ignition power so turns off when key is taken out, and there alternator appears to be putting the right voltage back to the battery as well Cheers.