E39 battery drain

[kiethton]

Within 2 days of putting the BMW reset and recharged battery in its died again....

Likely cause?

[Sardonicus]

kiethton said:

Within 2 days of putting the BMW reset and recharged battery in its died again....

Likely cause?

How old is the battery?

[kiethton]

18 months, had it back from BMW this weekend apparently fixed after the RAC said it was fubar - still under warranty

[58warren]

Could be a faulty 'hedgehog' unit draining it...

[kiethton]

This was my thought, however...the fan seems to behave itself?

One thing I have noticed was that the night before it went flat (every time it's done it) I've heard a car alarm...starting to think it may have been mine...

Would a hedgehog cause this?

If I was to get a new one is it best to go OEM or pattern? - £20 vs. £90

[RichardM5]

Common caused of batter drain in the E39 include :

Hedgehog or FSU, the fan can still be working fine, it just draws power when it should be off.
Old Telephone modules.
The Traffic Master system.
Faulty bonnet switch causing the alarm to go off.
Any 3rd party iBus device, iPod interface, USB etc. keeping the car 'awake'.


There are others, but these are the most likely candidates. Diagnostics is not hard, but can be very time consuming. Ideally you need to measure the current draw and leave the car to enter sleep mode (15 minutes). Pull a fuse at a time until you isolate the draw, but you have to leave the car to go back to sleep every time. Due to the time involved, you'll need to keep the car connected to a battery charger.

[kiethton]

Thanks for that, my car has all of those....think I need a multimeter and trickle charger!