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Discussion Starter #1
I have been chasing down a nasty battery drainage issue which kills the car if parked even 48 hours. It's almost untraceable, since when I measure the current off the battery when parked, it always falls to 0.020 A after a few minutes. The car charges up fine when driving, the battery is up to 12.6V when parked right after a drive. And it's a new battery.

While I haven't actually resorted to sleeping next to the car and measuring amperage over the entire 48 hours, I am totally lost as to where to look for the power draw - it must be at least 2A or so. I have checked current at the fuses too, but most turn up with nothing after a minute on the meter.

What are the usual suspects on the M5 for battery drainage? All interior lights are good, by the way, including the trunk. I do notice that with each disturbance, i.e. hood switch, trunk, door, etc...I get a 1A or so reading, which tapers off after a minute...assuming that is the central locking/alarm system.
 

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I have been chasing down a nasty battery drainage issue which kills the car if parked even 48 hours. It's almost untraceable, since when I measure the current off the battery when parked, it always falls to 0.020 A after a few minutes. The car charges up fine when driving, the battery is up to 12.6V when parked right after a drive. And it's a new battery.

While I haven't actually resorted to sleeping next to the car and measuring amperage over the entire 48 hours, I am totally lost as to where to look for the power draw - it must be at least 2A or so. I have checked current at the fuses too, but most turn up with nothing after a minute on the meter.

What are the usual suspects on the M5 for battery drainage? All interior lights are good, by the way, including the trunk. I do notice that with each disturbance, i.e. hood switch, trunk, door, etc...I get a 1A or so reading, which tapers off after a minute...assuming that is the central locking/alarm system.
I have never had the problem with my M5 but I have had similiar problems with a few vehicles I have owned previously with aftermarket audio and alarm systems.
 

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The car takes approx. 16 minutes to go to sleep. At this point you should have less than a 50mA draw on an E39.

Normally it's at or around 30mA.

Ever noticed any variation on the blower motor speed in the car? Normally a final stage unit is pretty obvious when it fails.

Sometimes they won't turn off at all, other times fan speed will vary when set, etc.

Common causes= aftermarket items, BMW telephone, CD changer...

Check there first. It sounds like this may be a tough one being it's sporadic. Not easy if you don't have the necessary equipment IE. being able to force the car to sleep.
 

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Discussion Starter #4
The car takes approx. 16 minutes to go to sleep. At this point you should have less than a 50mA draw on an E39.

Normally it's at or around 30mA.
I read 22 mA by connecting the battery negative through a calibrated Fluke meter on the 10A ammeter terminals. It's a little dicey since when I open the door the steering column triggers 12A or so for a second, not enough time to blow the fuse though.


Ever noticed any variation on the blower motor speed in the car? Normally a final stage unit is pretty obvious when it fails.

Sometimes they won't turn off at all, other times fan speed will vary when set, etc.

Once during a hot summer day last year, my blower wouldn't run at all. All other HVAC controls were running, but no blower. I started cursing yet another broken part in the car...but then it started running again 20 minutes later. I would have forgotten about this until you asked. Hasn't happened since, and the blower sounds like it's off when the car is off.


Common causes= aftermarket items, BMW telephone, CD changer...

Check there first. It sounds like this may be a tough one being it's sporadic. Not easy if you don't have the necessary equipment IE. being able to force the car to sleep.
I have no aftermarket anything in the car, except the guy before had a old phone charger hard-wired in.


Still perplexed. What system could fire up once the car is already asleep...? Without triggering the alarm...?
 

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I found in mine it was the phone contorl module.
 

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What does "kills the car" mean? That it won't start, or that you have measured the battery and it is below 12.5V after 48 hours?

If it is the former, then I would suspect your starter, either the motor itself or possible the relay.

If it is the latter, then all you can do is keep checking with your voltmeter, but if you are trying to tell us that you have 0.02A for the full 48 hours and then your battery is dead, you need a new battery.

d-
 

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The car charges up fine when driving, the battery is up to 12.6V when parked right after a drive. And it's a new battery.
I believe a new battery should charge to 13.7 or 13.8 volts. Mine does (original battery).
 

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I believe a new battery should charge to 13.7 or 13.8 volts. Mine does (original battery).
I think that's a bit high john - I've only seen 13.7/13.8 on most cars while running.

Steady state, car off, anything above 12.6V is considered 100% charged (a car battery is actually six 2.1V cells - thus 12.6V).
 

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I think that's a bit high john - I've only seen 13.7/13.8 on most cars while running.

Steady state, car off, anything above 12.6V is considered 100% charged (a car battery is actually six 2.1V cells - thus 12.6V).
Actually, you are right Doug. That's what I saw in the console message area while running ... It never occured to me that it would be different with the engine off. But, I'm NOT an electrical guru.

... well, I guess I'll go to bed now and pull the covers up over my head ...

John.
 

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Discussion Starter #11
After 48 hours, voltage is mid to low 11s and the car wont start, there's not enough power to lift the steering column when the door opens.

The running state is 13.6V or so (when above idle...idle shows in the high 12s - I think this is normal).

The unused phone charger seems fine, it doesn't pull any current on the fuse. I even pulled the rechargeable flashlight just in case...but that doesn't seem to make any difference.

I will pull the phone charger and see if it makes a difference at all.
 

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We do not have "deep cycle" batteries.

If you have taken it down to the low 11's you now need a new battery as it willl no longer hold a charge. Doesn't matter how long you run the car, the battery simply isn't going to charge.

Replace your battery (again) and report back - I'd bet your problem is solved.

d-
 

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NEW batteries can fail ... I know ... it happened to me. (NOT in the M5, though.)
 

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We do not have "deep cycle" batteries.

If you have taken it down to the low 11's you now need a new battery as it willl no longer hold a charge. Doesn't matter how long you run the car, the battery simply isn't going to charge.

Replace your battery (again) and report back - I'd bet your problem is solved.

d-

Hmmm - it seems to charge up fine...it charges on a 10A charger to 12.6V. And the car will start, even down to low 12s V. I thought the battery is fine, in my opinion, but I am no expert in batteries...

But are you saying it won't hold this charge afterwards...? And the voltage would drop after it has been charged since it was drained a couple times? So there is no mystery leak, it's just that my new Exide battery blows? The same thing was happening with my old Douglas battery, but it was the original from 2000, which is why I changed it a few months ago.

The best deal I could find was from Budd's BMW, $300 installed, not that I had any problems installing, but they would not sell it cheaper otherwise - actually would be $10 more. They were carrying Exide and not Douglas anymore, they had too many problems with the Douglas. I guess I can go back for warrantee...I think it's a full replacement within the year.

Anyway, I'll do a longer test soon and report back my amperages and voltages, this time over a few hours at least.
 

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Look in the FAQ - there is a writeup there on how to appropriately test your battery. It has something to do with leaving the headlights on for a period and then checking voltage.

You can almost always charge a battery back up to 12.6V - the question is whether or not it will stay there.

Bad batteries do occur, but I'm not saying this one was or was not manufactured badly, I'm just saying that based on what you've written I think it is bad now.

Have you checked your alternator to make sure it is putting out an appropriate charge while running? If you can't get 13.7V+ while the engine is running then you need to look at a new alt / voltage regulator. You should be getting somewhere in the 14V range...

d-
 

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0.020A when parked is perfectly normal. The "new battery" comment is virtually meaningless...it will become junk once drained a few times.

If you're only seeing 12.5 volts when running, your charging system is absolutely defective. The battery will not charge at that value. You must see over 13 volts when running, if the charging system is healthy. It could be a bad alternator, regulator or many other things.

Siounds like you need to fix the charging system and then buy a new battery. Don't treat the symptom first by buying another battery. Driving around like this for a week or so will suck all the life out a month old battery. Your electronics are also taking a terrible beating with this recurring undervoltage condition.

My advice is..take the car to a dealership before you wipe out a couple $500 modules.
 

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0.020A when parked is perfectly normal. The "new battery" comment is virtually meaningless...it will become junk once drained a few times.

If you're only seeing 12.5 volts when running, your charging system is absolutely defective. The battery will not charge at that value. You must see over 13 volts when running, if the charging system is healthy. It could be a bad alternator, regulator or many other things.

Siounds like you need to fix the charging system and then buy a new battery. Don't treat the symptom first by buying another battery. Driving around like this for a week or so will suck all the life out a month old battery. Your electronics are also taking a terrible beating with this recurring undervoltage condition.

My advice is..take the car to a dealership before you wipe out a couple $500 modules.

For sure I see high 13s V when running, see my prev. post. But definitely only mid-high 12s when idling, I think this is perfectly normal, no? I did a few searches on load testing the battery, there was nothing in the FAQ but I did come up with a few old posts:

http://www.e38.org/battery.pdf
http://www.m5board.com/vbulletin/showthread.php?t=101637&highlight=battery+test
http://www.m5board.com/vbulletin/showthread.php?t=63555
http://www.m5board.com/vbulletin/showthread.php?t=101122

I did a load test by turning on headlights + high beams for 5 minutes...voltage dropped 0.5A to 12.0V when it was done. It's marginal, I'd say, but I guess it could be the battery. Still I can't see how it died in the first place after the new battery was installed. I haven't changed/added anything electrical and I still read the 0.02 A when parked after everything settles.

I will get the battery swapped at the dealer, I'm pretty sure warranty gives a full replacement within a year, after that it's pro-rated to 5 or so years. It could very well be the battery...but then it must have been defective since the start. The "New Battery" comment is not totally meaningless to my wallet!

Thanks everyone for your help.
 

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While I agree with John, if you are seeing HIGH 13's w/ a digital multimeter while running (high 12's at idle is fine, but it has to be above 12.7ish) then it sounds like your charging system is ok. Nevertheless, Autozone offers free testing, so if I were you I'd take them up on it, and then go get a new battery.

Bad batteries from the factory do happen, but they are rarely enough that you should ensure there is nothing else wrong before replacing it.

d-
 

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recently, i had a similar situation in my suburban. Battery was less than a year old. I went thru the whole process of removing every fuse, checking seats, aftermarket video, etc. Turns out to be the battery. It would charge fine last all day driving around, and then run down overnight.

When you hear hooves think horses not zebras!

Take the battery out of the car charge it, let it sit a day or so and test the charge. Or get a load tester and test it.
 
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