I've been battling this issue for about 6 months now, finally decided to see if anyone had any ideas. While parked, our car will drain the battery at a rate of ~0.3V per day. This typically leaves the car unable to start in 3-5 days.

I know the battery is being charged properly as it will read 12.6ish volts if Ive been driving it. The battery is only about 4 months old (thought the old one was bad, may have been fine) and tested normal at Autozone. Back in the winter I did find that fuse FL11 (radiator fans) was blown but this may be unrelated as it hasn't blown since. I've tested the parasitic draw by bridging the positive lead with the positive terminal on the battery using my multimeter. It reads 0.1mA which doesnt seem like much to me.

I was reading that a wet BCM may cause issues and might be getting wet due to leaking windshield seals. I'm pretty sure our windshield does leak a little as I've seen water trails through the dirt/dust on the inside of the windshield. I started to pull the BCM but had some trouble and stopped since I didn't want to break something and make the car completely undrivable. We have had some heavy rains in the last few days and the carpet/wiring around the BCM felt completely dry.

I'm stumped on what to try next. I was thinking of pulling fuses 1 by 1 and checking the parasitic draw but that's all I got. Any help would be appreciated because this is driving me batty!

 

That 12.6 volts you are getting are you testing it while its running?

 

Mine was doing the same thing. It ended up being a loose battery cable. I tightened it and now it is fine. It's worth a shot if you have not checked them.

 

Motor off, battery both in and out of the car.

As for the cables, think I've had them on and off about 100 times in the last 6 months! They're tight!

 

If you know your cables are clean and tight then it can get a little tricky on finding whats draining the battery. I would take your volt meter and see what volts your getting while its running. Did you ever look at your BCM? other wise you might have to go with your plan of pulling fuses one by one..

 

Do you 'lock' the car when you park it? If not, remember that there are electronic things operating while you are away and they will use up part of a battery.

 

You SHOULD be able to go about 2 months without using your car and still start it...I have..due to one VERY long trip I took....
There are a few posts about how to monitor drain on individual circuits...
OPTIMA Jim posted it (the battery rep from said company...
Sounds like you need to figure out if you have a light on or other drain.....
And just a reminder...a GPS, Radar dector, or other item left on can cause issues....so UNPLUG EVERYTHING!!!
A few folks had the competitor to the scanguageII installed...and had this issue...make sure EVERYTHING IS OFF!!

 

Car is always locked, don't see any interior lights on. The only accessory we had in the car was an ipod connector. I left that unplugged for a week but no such luck.

Thanks for the heads up on the thread, I'll search for it. Would be nice to be able to test each circuit instead of pulling a fuse and running to check the multimeter.

 

Could be a long shot, but by any chance is it parked near another modern car with an perimeter alarm system? One that could have been designed by BMW? Could your car keep "talking" to the other alarm system? Or is there any source of magnetism really close by, like a utility company "green box" transformer? Neighbor have a massive shortwave antennae tower in their yard?

 

Ha, no, the car isnt ever near anything when parked. Nothing is a long shot when it does to electrical problems though!

I was able to find the video from optimajim. The end result is the same, pull fuses and heck the draw.

 

Did you ever figure it out?