Battery draining while off

Well here is one I've never had to deal with before...

Something is draining my car to a point so low that the gauges don't even flicker when I turn it to the run position. And it's not consistent either.

A few times I have let the car sit over night at home for 12-14 hours, and it has full power in the morning. On those same days, the car has nothing left in it after I'm at work for 8-9 hours. Putting aside the possibility that my car and I have developed a symbiotic relationship with regards to energy, does there exist a common set of occurrence for this problem in our E30's?

Alternator and battery appear to be fine. Battery isn't even a year old. I've looked around the car and nothing is visibly/audibly stuck on. I'm guessing something is shorting out someplace...

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Hook up a meter or test light in line between the battery ground and battery. Start pulling fuses, when the light dims or the meter shifts, you have found the circuit which is the culprit.

alan

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alanrw
Hook up a meter or test light in line between the battery ground and battery. Start pulling fuses, when the light dims or the meter shifts, you have found the circuit which is the culprit.

alan

Brilliant! And my brand new digital multimeter just arrived in the mail yesterday

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

Realize that certain circuits like the radio or clock will draw a small amount. You could set you multimeter to amps and see what is drawing enough amps to pull down the battery. It won't be the clock or radio.

And oh yeah, remembering a comment by either Rick or Peter a while back, check the trunk light. Sometimes it stays on even though the trunk is shut.

alan

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alanrw
Realize that certain circuits like the radio or clock will draw a small amount. You could set you multimeter to amps and see what is drawing enough amps to pull down the battery. It won't be the clock or radio.

And oh yeah, remembering a comment by either Rick or Peter a while back, check the trunk light. Sometimes it stays on even though the trunk is shut.

alan

Well....no luck. I believe everything must have been working correctly when I did my test.

I was losing 44 mili amps, which I was pretty sure was nothing, but I started pulling fuses for the fun of it anyway.
Sure enough, the two fuses that accounted for almost 30 mA of that were the IC, ECU, and OBC (apparently only devices with acronyms draw power).
For reference, having the key in the start position draws 5 amps, and I'm pretty sure my battery can do that on a normal day for hours on end. 44 mA sounds like a standard draw to me. Not sure what the amp-hour rating of our batteries is, but a quick google produces results for some car batteries around 40 Ah.
So yeah, 44 mA is not my problem...

I guess I'll just keep checking it and see if I can shake whatever wire/device is doing this into the wrong position again.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil

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alanrw
Realize that certain circuits like the radio or clock will draw a small amount. You could set you multimeter to amps and see what is drawing enough amps to pull down the battery. It won't be the clock or radio.

And oh yeah, remembering a comment by either Rick or Peter a while back, check the trunk light. Sometimes it stays on even though the trunk is shut.

alan

Well....no luck. I believe everything must have been working correctly when I did my test.

I was losing 44 mili amps, which I was pretty sure was nothing, but I started pulling fuses for the fun of it anyway.
Sure enough, the two fuses that accounted for almost 30 mA of that were the IC, ECU, and OBC (apparently only devices with acronyms draw power).
For reference, having the key in the start position draws 5 amps, and I'm pretty sure my battery can do that on a normal day for hours on end. 44 mA sounds like a standard draw to me. Not sure what the amp-hour rating of our batteries is, but a quick google produces results for some car batteries around 40 Ah.
So yeah, 44 mA is not my problem...

I guess I'll just keep checking it and see if I can shake whatever wire/device is doing this into the wrong position again.

You are correct, anything under 50mA is perfectly normal.

Don't be too sure your new battery is a good one. My last battery died after about 4 months or so. I took it back to where I bought it and they put it on a tester...sure enough, it had a dead cell

With a full charge, your battery should have at least 13.V charge.

One other thing to check is the main ground straps; at the battery, at the terminal post on the fire wall and the one that goes from the engine block to the chassis.

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Archeo-peteriX

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Earendil
I guess I'll just keep checking it and see if I can shake whatever wire/device is doing this into the wrong position again.

You are correct, anything under 50mA is perfectly normal.

Don't be too sure your new battery is a good one. My last battery died after about 4 months or so. I took it back to where I bought it and they put it on a tester...sure enough, it had a dead cell

With a full charge, your battery should have at least 13.V charge.

One other thing to check is the main ground straps; at the battery, at the terminal post on the fire wall and the one that goes from the engine block to the chassis.

I haven't discounted the battery, but I don't think it can be the root of my problem.
The battery, if dieing, should not one day lose its entire charge in 8 hours, and then 24 hours later be good for 14 hours. And yes, in both cases the car was run long enough to fully charge the batter.

A dieing battery could however be an indicator for another problem. It could be that I've had a drain for some time now, and a weaker battery is letting it show through in a shorter period of time.

I thought most car batteries were rated around 12.5-12.6 and that with the alternator you'd see 13+ ? Pretty sure my battery isn't pushing beyond 13 volts...

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

I've got a weird one in Janet's car; sometimes the obc will come on (with the key off) and drain the battery (a Benz diesel battery) and sometimes it's fine. When I'm waiting for her sometimes in the car reading, that obc just comes on at random... scary, and a pain in the ass

I put a battery idolater on the battery post but that's not going to cut it forever!

Try sticking a low amp battery charger on your battery with it still connected to the car. After eight hours of charging pop the hood open and feel the alternator. If it is warm then it needs replacing and that is where your draw is coming from. The alternator may still test good on all counts and be charging the system fine, but it is bad! Also, sometimes the car if it is usually driven for short trips is not able to maintain the charge of the battery as you are using more power to start the car than is replaced while driving a short distance. Over time this will lessen the charge of the battery and you need to periodically throw a charger on it to maintain a healthy charge. If allowed to stay in the lowered charged condition for a long period of time the battery loses its ability to keep a full charge which should be above 12.8 volts. Your battery may also be suspect at this point too!

Well, I made it to the 300 miles to Spokane without incident. In fact, I was reminded once again how much of a blast these old cars are to drive. It was windows down the whole way

I didn't know the alternator could be tested in that way. With all the coolant that had escaped from various hoses recently, I know the alternator has been drenched, while running. And my battery was only pushing up to 12.76, so we'll see if the long solid drive pushed it higher.
I believe my neighbor back home has a trickle charger, I should be able to use that.

Still seems odd that this drain would come and go though...

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil
Well, I made it to the 300 miles to Spokane without incident. In fact, I was reminded once again how much of a blast these old cars are to drive. It was windows down the whole way

I didn't know the alternator could be tested in that way. With all the coolant that had escaped from various hoses recently, I know the alternator has been drenched, while running. And my battery was only pushing up to 12.76, so we'll see if the long solid drive pushed it higher.
I believe my neighbor back home has a trickle charger, I should be able to use that.

Still seems odd that this drain would come and go though...

That alternator test is new to me also, I'll have to ask my electrical shop man about it. The fact you have an electrical gremlin that comes on goes is not so unusual; its like my OBC draw short that comes and goes, or my car that won't start on rainy days- but this morning (it was raining all night) started fine

It's electrical and it doesn't have to make sense (I find myself saying the same thing about family sometimes...

Rick

All the way Spokane and back without an electrical hitch of any kind. Damn...

Perhaps I need to plan to go someplace important, with only a few minutes to spare. That should guarantee the return of the electrical demon, right?

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

I had a situation like this a few years ago. The problem was that it was winter and I would drive to work with the heater and the lights and wipers on, the battery would barely start the car after work. Driving home it would get charged up and start ok the next morning. After replacing the battery and having it fail in a few weeks it turned out to be the alternator that was only capable of charging at a low rate due to partial failure of the diode pack. It would check out ok on a voltage check but would not run all the accessories of the car. Went thorough two alternators because the new alternator was overloaded by the then damaged battery. Had to change both at once to cure the problem.

Bob in Everett

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Bob in Everett
I had a situation like this a few years ago. The problem was that it was winter and I would drive to work with the heater and the lights and wipers on, the battery would barely start the car after work. Driving home it would get charged up and start ok the next morning. After replacing the battery and having it fail in a few weeks it turned out to be the alternator that was only capable of charging at a low rate due to partial failure of the diode pack. It would check out ok on a voltage check but would not run all the accessories of the car. Went thorough two alternators because the new alternator was overloaded by the then damaged battery. Had to change both at once to cure the problem.

Bob in Everett

Common problem (what I've seen through the years). Electrics are tender, fickle little beasts.

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rkj

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Bob in Everett
I had a situation like this a few years ago. The problem was that it was winter and I would drive to work with the heater and the lights and wipers on, the battery would barely start the car after work. Driving home it would get charged up and start ok the next morning. After replacing the battery and having it fail in a few weeks it turned out to be the alternator that was only capable of charging at a low rate due to partial failure of the diode pack. It would check out ok on a voltage check but would not run all the accessories of the car. Went thorough two alternators because the new alternator was overloaded by the then damaged battery. Had to change both at once to cure the problem.

Bob in Everett

Common problem (what I've seen through the years). Electrics are tender, fickle little beasts.

Especially if those electronics were put into a perferated hunk of high speed metal that insists on high frequency vibrations...22 years ago.

Anyhoo, the Electrical demons have vanished for no apparent reason. I can't decide if that's a good thing or not... It'd make me feel better if it wasn't my only vehicle

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

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Earendil

Quote
rkj

Quote
Bob in Everett
I had a situation like this a few years ago. The problem was that it was winter and I would drive to work with the heater and the lights and wipers on, the battery would barely start the car after work. Driving home it would get charged up and start ok the next morning. After replacing the battery and having it fail in a few weeks it turned out to be the alternator that was only capable of charging at a low rate due to partial failure of the diode pack. It would check out ok on a voltage check but would not run all the accessories of the car. Went thorough two alternators because the new alternator was overloaded by the then damaged battery. Had to change both at once to cure the problem.

Bob in Everett

Common problem (what I've seen through the years). Electrics are tender, fickle little beasts.

Especially if those electronics were put into a perferated hunk of high speed metal that insists on high frequency vibrations...22 years ago.

Anyhoo, the Electrical demons have vanished for no apparent reason. I can't decide if that's a good thing or not... It'd make me feel better if it wasn't my only vehicle

If it ain't broke don't fix it- I'm sure you'll get the chance soon enough

Intermitent problems are very annoying.
Those are often caused by bad contacts, aged wiring and connectors, rusted terminals, you name it.

Most places to look were described above, better is to keep the battery charge up with the external charger, and keep the battery jumper cables in the trunk, to be on the safe side.

Once I fried the Renault Clio alternator after starting a MB class C from a friend.
It worked fine that day, few weeks latter the red light from the alternator came on, sure enough the diode board tested bad.
The battery goes on, after I charged it, it was three years ago.

Good luck!