I have experienced intermittent complete battery drain overnight for nigh on 5 years. Does not happen very often. Sometimes I can leave the car parked for 2 weeks while overseas and it is fine, then sometimes with normal daily driving - overnight the battery can go flat. But this happens maybe once very 6 or so months. No idea what the cause and hard to isolate due to the intermittent nature. So I bought an automatic battery isolator.
When the battery drops below 11.9 volt it disconnects the battery. It is not relay based but FET based. I had to remove some of the polystyrene next to the battery to fit it but not a big deal. I was worried that starting the diesel would run over the 350amp peak current rating but all is good so far. ie the X3 starts fine with the isolator in circuit.
So now if the dang thing that is draining the battery has its wicked way it will not kill the battery . . . in theory.
The only problem then is if this happens, I have to access the battery with no power on the car to press the reset switch to re-connect the battery and hopefully start the car. Yes this is possible ie the rear hatch can be accessed with no power in the car.
Not the best solution - the best is to isolate the cause of the intermittent drain - but it may provide some added insurance.
Time will tell . . . . .
VW Touareg V6 TDI 4Motion
X3 3.0d 2006 (MY07) being sold
Last edited by x3oiler; 09-03-2011 at 02:01 AM.
Reason: Link bad - fixed