Parasitic Battery Drain

[jsevd]

Death by pin pricks recently

A week ago my battery went dead on my 93 318is. At the time I assumed that I left the lights on or something to that effect, so since the battery was getting up there in age I elected to just buy a new one (not cheap at $89).

Put the new battery in, and did not drive the car for a few days, and low and behold the battery was dead again. Jumped the car, drove it for 20 minutes, and it ran fine. Parked the car, left it for a few hours and it started right up again and drove about 30 miles, so this seems to rule out the charger system or the battery itself.

Left it overnight, and low and behold it went dead. Jumped it one more time, let it idle for 30 minutes to charge the battery, and this time I disconnected the negative post.

Next morning reattached the post and the car started right up. Bingo, it appears something is leaching the battery back down to 0 in about 12-24 hours.

Tried all obvious angles, such as the radar, radio, dome lights, glove box, engine fan still running, etc. and all appear to be in order.

Any suggestions on where else I can look? For now, I am simply disconnecting the (-) post each night and then reattaching in the morning, but I cannot keep that up for ever, so before I plunk down any hard cash on a diagnostic by my shop, I am hoping that someone might have some good feedback.

Thanks for any advice.

 

[wood_e]

There may be an improper ground on the car, or more lkely you need a new alternator. If oyu have an aftermarket alarm that could be a culprit...

 

[Kirby]

- Have you made any changes to the electrical system recently? Amps, lights, etc?
- You said that you checked all the obvious stuff - radio. etc. Did you disconnect all aftermarket stuff, by unwiring, pull the fuse, whatever. Does it still suck the battery down?

If you have a voltmeter you might find the circuit by attaching the voltmeter to the battery. Pull fuses one at a time. If there is something pulling a fair amount of current, you will see small voltage INCREASE when you pull the fuse for that circuit. Keep in mind that some devices, like the radio, normally draw a small amount of current all the time. But if you are draining the battery overnight, it's sucking more than just a little current.

If you can identify a particular circuit, then figure out what equipment is on that circuit, and disconnect each one separately, if possible.

 

[jsevd]

Good logic. I can borrow a mutilmeter from a friend in my IT department and begin the methodical process you described above.

I will post results once I nail the leaching offender.