Battery Drain - Common Causes

brotherhay · Post by **brotherhay** » Fri Sep 02, 2011 2:15 pm

Just put in what has to be about the 4th battery in 10 years into my ' 80 528i.

In the past there were a few things that were wired improperly. The main source was the Radio. After market, wired hot wrong, bad ground. That has been taken care of but still I have a slight drain. If the car sits 2 weeks, It will still have some decent voltage left in it, but not enough cold cranking amps to get the starter turning. Also checked to see if the alternator was charging properly, it is. Started with the battery at about 3v this morning, ran it for maybe just 5 miles, checked again, 11.5v. 14v while running.

So, I am going to give it another once over. I suspect either the ground strap or even cable itself might be ready to be replaced.

What other common problems are there?

Keith · Post by **Keith** » Fri Sep 02, 2011 3:11 pm

Best thing to do is put a mulitmeter over each circuit on the fuse box. See if any of them are pulling any amps when the car is off. When you find which one it is, you should be able to narrow it down to whatever is on that circuit. The most common ones I've had are the glovebox light, trunk light, and the power locks staying energized. The only draw you should have while the car is off is a few millivolts to the circuit that powers the analog clock.

brotherhay · Post by **brotherhay** » Sat Sep 03, 2011 4:37 pm

You know, I never even thought of that, obviously, ha.

Yes, with that in mind, this should not be hard at all.

Thanks for the tip, that should come in quite handy from here on out, on any vehicle.

brotherhay · Post by **brotherhay** » Sun Sep 04, 2011 12:51 pm

Checked it today, and it seems I have 3 fuses pulling 12 volts when the car is off.

Cigarette Lighter/Power Antenna
Hazard warning system/glove comp/clock
and
Supplementary Fan

The fan I have never seen turn on until the car is super hot
no power antenna, and I dont smoke
warning buzzer has never worked, i didnt even think there was a glove box light. And Im sure the glove box charger doesnt work either.

So, Ill pull all 3 and deal with that for now. But geez, what a mess Ill have to track down there.

Keith · Post by **Keith** » Sun Sep 04, 2011 5:54 pm

Well the real culprit is when you have a significant amp draw. Even .5 amps will drain the battery pretty quickly. Take a look at that also.

Mike W. · Post by **Mike W.** » Mon Sep 05, 2011 9:32 am

brotherhay wrote:Checked it today, and it seems I have 3 fuses pulling 12 volts when the car is off.

Cigarette Lighter/Power Antenna
Hazard warning system/glove comp/clock
and
Supplementary Fan

The fan I have never seen turn on until the car is super hot
no power antenna, and I dont smoke
warning buzzer has never worked, i didnt even think there was a glove box light. And Im sure the glove box charger doesnt work either.

So, Ill pull all 3 and deal with that for now. But geez, what a mess Ill have to track down there.

I suspect you are measuring voltage, not current. You have found which circuits are always hot, not what is drawing power. You need it set on amps, starting with the 10A setting, then measure the current inserting the meter in line with the circuit, across the fuse contacts, not from the fuse to ground.

brotherhay · Post by **brotherhay** » Mon Sep 05, 2011 7:14 pm

I metered it by holding a lead to one side of the barrel fuse clip, and the other lead to the other clip end. Nothing seemed to be drawing anything.

The 10 amp setting on my multimeter requires that you switch the positive lead to a separate 10ADC connection. I did do that, if anyone was wondering.

Since I have no glove box light, I will also check the battery charger in there. I suspect that doesn't put out anything. Those are my main culprits.