The above battery isolator is a bust. Worked for a while but too many bad effects on the car electronics due to lower voltage during cranking . . then it blew up anyway - went into permanent open circuit.
Originally Posted by x3oiler
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 . . . . .
I have traced my intermittent battery drain to the stock business CD head unit or the aftermarket parrot blue tooth module that connects to it. ie one or the other is not always turning off. But the GPS that is powered via the head unit gives a good indication so I can catch the problem. ie the GPS does not sometimes turn off with the ignition. Turn head unit on then off (after ignition of) and GPS goes off and I know the suckers are now shut down. So readers with un traced battery drain might consider manually turning off the stereo before turning off the ignition at least for a time. If no longer an issue then it will be the HU at fault.
X3 3.0d 2006 (MY07)