BMW M5 Forum and M6 Forums banner

The Beast eats batteries for breakfast!

1572 6
Hey guys,

I'm kinda stuck with a one year old problem that's eating batteries like cookies. I kept having problems starting the car after parking it 8-10 hours which let to numerous dealer and self troubleshoots, new batteries, new fan relays, current drain tests etc...

Long story short, I just purchased a new battery since the old one was nuked due to several discharges.

- New battery's voltage at the shop was 12.62v and the 'eye' was green.
- New battery with the car turned on shows 14.2 - 14.6v thus alternator/charing system should be OK.
- New Battery voltage after a 10-15min drive is 12.6v (12.72 sometimes, 12.8v)
- I Hooked up an meter in series and checked the drain which was at around 3A then after 15 minutes it was 0.02A both with the alarm on and with the alarm off. I glanced at it several times over the course of 2-3 hours and it seemed to stay around the 0.02-0.03A range.
- Sometimes while the car is parked armed, the alarm still randomly goes off.
- After parking 8-10 hours, the battery shows around 12.5v, slightly lower than a full charge.

All this leads me to believe there's an intermittent problem that wakes the car *sometimes* and that's slowly eating the battery. In case the drive wasn't long enough to full charge the battery, the battery can drain during the time that it's sitting parked. After a couple discharges the battery is as good as dead.

My hope is to not drain this brand new batt. Any troubleshooting suggestions? I'm thinking pulling 1 fuse per night and seeing if in the AM there's a lower voltage than in the evening. Can you suggest which fuses are the common culprits that I should start with?
1 - 1 of 1 Posts

· Registered
Joined
·
136 Posts
Check the usual like your final stage?

Have a meter that makes an audible alert if it goes over a set range? (i.e. 0.02A)

I would start with pulling fuses of main components that are unneccessary, like the NAV, IHKE, etc.

Another thing to consider but I don't have a lot of information on right now is that there was something somewhere once when I worked at BMW that talked about a certain component waking the CAN bus randomly. I don't remember exactly what it was but for some reason I think it was due to a faulty Nav computer.
 
1 - 1 of 1 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top