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Thread: Battery Draining Completely Overnight

  1. #1
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    Battery Draining Completely Overnight

    Before I start, yes I’ve searched this up and can’t seem to find anything that resembles exactly what I’m experiencing.

    The car is a 97 328i. It sat for a few months not being driven over the winter. I started it up every few weeks or so and let it run for about 15 minutes. Never had a problem starting. A few weeks ago I took the car for a short drive, probably 5 miles or so. I then parked the car in the garage so I could replace the subframe and differential bushings. When I put the car back on the ground and put the key in, it was completely dead. No noises, lights, nothing. You wouldn’t know it was even connected to a battery. I went and tested the voltage across the battery in the trunk and found it sitting at 3.6 V. Immediately hooked it up to a charger, got it charged back up, and then it was fine after that.

    Yesterday morning I went out to the car and immediately knew something was wrong when I stuck the key in the door. I turned the key unlocking only the driver’s side door. The central locking system did nothing. I opened the door to see no interior lights on. To no surprise, the turn of the key in the ignition did nothing. The car was sitting lump with absolutely no power.

    Being at school and not at home, I did not have access to a battery charger or even a multimeter. The first idea I had was to jump it. A friend came and let me jump it off his car. I got the car running and left it hooked up for a few minutes to let the battery charge back up. I then unhooked it and took the car for a drive. Everything seemed fine until I reached a traffic light.

    The radio stopped. First thinking it was just my phone I looked down and the screen on the display turned off. Immediately I looked to my cluster and watched as the tach dropped to 0. The car died in the middle of the road, and no electronics worked at all.

    To my surprise it’s not hard to push these cars around by yourself, so I pushed it around the corner into a parking lot, and called up my friend again for help.

    The battery was just over a year old but with it being drained down that much a few times now I figured it would be better to just warranty it out. I took the battery to Walmart, swapped it for a new one, and put it in the car.

    The car started right up. I drove the car back to my apartment and parked it. I then went to work, and then returned 6 hours later. The car started right up. I let it sit another 3 hours or so, and then started it up and drove it to AutoZone to have an alternator test ran.

    They hooked their machine up to the battery and read that the battery was good with the car off, but with the car running it was showing right around 12V. Not good....

    The diagnosis from that was an inadequate alternator. According to the manager there, it was just enough to keep the battery at its currently state. Pretty much saying, each time I start the car, it’ll drop in voltage. So eventually, it’ll drop so low the car won’t start. I planned on replacing it this weekend when I’m home, but the car had other plans for me.

    This morning I came out to the car to find the car in the same state it was in yesterday. Completely dead with no sign of life. So far that’s all I’ve done for today, I didn’t have time to mess with her, I had to get to class.

    I can’t say I’m surprised she’s acting up. After all I just bought a 95 M3 that I’ve been wrenching on so she’s probably just jealous and being stubborn.

    Anyways, any help or advice would be greatly appreciated. I know I need to replace the alternator, but to me, I don’t see how the battery could completely drain overnight from that being the problem. Even a small constant draw wouldn’t bring a battery that low in 10 hours. My guess is a short somewhere, but I’d like to know what the masses think. Thanks

  2. #2
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    I don't really trust autozone and their "Magical battery testers" Too many times i've gone there for them to tell me my battery had a dead cell or the alternator was good and it was quite the contrary. Search on youtube how to do a drop voltage test. That should for sure eliminate shitty wires, bad battery, bad alt etc... then head from there.

  3. #3
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    Quote Originally Posted by channing93 View Post
    I don't really trust autozone and their "Magical battery testers" Too many times i've gone there for them to tell me my battery had a dead cell or the alternator was good and it was quite the contrary. Search on youtube how to do a drop voltage test. That should for sure eliminate shitty wires, bad battery, bad alt etc... then head from there.
    Could it be as as simple as a poor ground connection?


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  4. #4
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    Quote Originally Posted by Nate94 View Post
    Could it be as as simple as a poor ground connection?


    Sent from my iPhone using Tapatalk
    Yeah unfortunately it could be as simple as that or complex and hard to trace. Electrical problems aren’t fun, I prefer mechanical ones

  5. #5
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    Quote Originally Posted by Nate94 View Post
    Could it be as as simple as a poor ground connection?


    Sent from my iPhone using Tapatalk

    Could be bud. Watch the video im attaching to this. The whole thing. You will save yourself so much future headache man. https://www.youtube.com/watch?v=DfLyh43iihM

  6. #6
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    Once you watch that video I want you to watch this video https://www.youtube.com/watch?v=QRso1A0VScw

  7. #7
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    Google final stage resistor hedgehog

    Then if pulling the heater fan fuses doesn't stop it you need to do proper investigation
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  8. #8
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    Quote Originally Posted by E36328Coupe View Post
    Google final stage resistor hedgehog

    Then if pulling the heater fan fuses doesn't stop it you need to do proper investigation
    I replaced the FSU just over a year ago but I’ll check it to be safe

  9. #9
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    A good electrical test that I learned is to put your voltmeter on Amps, disconnect the negative battery cable, and put the two terminals of the voltmeter from the negative battery cable and the negative battery post.

    This electrical current reading (in amps) will show how much of a draw is draining your battery overnight.

    Disconnect fuses or electrical components, and re-check the amps reading.

    Brian

  10. #10
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    Quote Originally Posted by Brian 328is View Post
    A good electrical test that I learned is to put your voltmeter on Amps, disconnect the negative battery cable, and put the two terminals of the voltmeter from the negative battery cable and the negative battery post.

    This electrical current reading (in amps) will show how much of a draw is draining your battery overnight.

    Disconnect fuses or electrical components, and re-check the amps reading.

    Brian
    And the reading should be ~0.02A, if it is more then check first all your lights in the car, try to disconnect the radio(i have same problem) and try remove one by one fuse to see result of current reading...
    Last edited by Bela27; 05-02-2018 at 04:33 AM.

  11. #11
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    Also check if the light in your trunk is turning off when closing the trunk lid. If you have no sight on the trunk when it’s closed, start a recording on your phone, put it in the trunk and then close the lid. Then just play the recording back and you’ll see

  12. #12
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    engine ground strap. check it. clean it. make sure it has good connection. thats probably it. if its off or has a bad connection the altinator cannot charge the battery or keep the demand of load change after the car has started. so the starter will drain the amps, while the poor connection cannot recharge the battery. Leaving you with a few starts and a few minutes of driving before the battery depletes and the car stalls.
    Nobody would recertify these machines after somebody screwed with them without any visibility into what they did.

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  13. #13
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    Parasitic battery drain. O'Reilly auto parts has a rental tool called the amp hound. I have used it in detail in another of my posts. It will tell you which fused circuit is draining your battery.

    In my case it was fuse 33. That one controls the interior lights. I eventually traced my battery drain down to my trunk light. It was very hard to do so, because the light comes on whenever the trunk is opened. My light was staying on all the time, but I didn't know because I thought it was just on from me opening the trunk to check it.

    I eventually found the problem because I removed my rear seats and ski pass to install a subwoofer. I noticed the light coming thru the ski pass when it shouldnt be. I removed the light bulb and boom problem solved.

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  14. #14
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    I appreciate all the replies but I just want to clarify that when I mean dead, the cars dead, and within the matter of hours. I have LED lights throughout the car so I’m pretty sure that one is out but I’ll still check anyways. The ground strap seems to be a likely cause so I’ll check that too.

  15. #15
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    Quote Originally Posted by jakelamp13 View Post
    I appreciate all the replies but I just want to clarify that when I mean dead, the cars dead, and within the matter of hours. I have LED lights throughout the car so I’m pretty sure that one is out but I’ll still check anyways. The ground strap seems to be a likely cause so I’ll check that too.
    Mine was going from 12.5 volts down to 0 overnight. It would go from fully charged to not able to start in about 30 minutes. I went thru 4 batteries and had to carry a jumper pack at all times until i found out why it was draining.

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  16. #16
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    Quote Originally Posted by XnWarden View Post
    Mine was going from 12.5 volts down to 0 overnight. It would go from fully charged to not able to start in about 30 minutes. I went thru 4 batteries and had to carry a jumper pack at all times until i found out why it was draining.

    Sent from my VS987 using Tapatalk
    That just doesn’t seem right to me if it was just an interior light being on. You can sit there for 30 minutes listening to your radio with lights on and the car will start right up, but then again anything is possible. I’ll test it tonight

  17. #17
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    Quote Originally Posted by jakelamp13 View Post
    That just doesn’t seem right to me if it was just an interior light being on. You can sit there for 30 minutes listening to your radio with lights on and the car will start right up, but then again anything is possible. I’ll test it tonight
    It didnt start out that bad. But along the way I had other things go wrong too, possibly even as a result of that faulty light. My engine ground strap stopped working and my battery cable got really corroded.

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  18. #18
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    Quick Update:

    I went out the car after having let the battery sit disconnected from the car overnight. It read 8.5 V on my multimeter. I then did a draw test on the battery by placing the multimeter in the 10ADC mode and then in-series with the negative lead of the car and the negative post of the battery. The draw was only 0.01 A at first but grew slightly over time. I then hooked the battery up completely and read the voltage across it.....less than 3 V.....

    What the hell?

    The battery is currently on a charger. I'm hoping my car didn't ruin it.

  19. #19
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    Autozone is right. You have a failing alternator.
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  20. #20
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    You should be using a battery charge. A dead battery is ~ 60 AH / 2 amp charger = ~ 30 hours on a battery charger

    If you use only the alternator that can be a problem, it charges until the battery voltage is up to ~13.5 V and with a dead battery you can get that false voltage with just a few amps of charge. ( plus you already got ...The diagnosis from that was an inadequate alternator. According to the manager there, it was just enough to keep the battery at its currently state. Pretty much saying, each time I start the car, it’ll drop in voltage. So eventually, it’ll drop so low the car won’t start.) You can also damage the alternator by over driving the circuits charging a dead battery.

    An intelligent battery charger will properly charge a depleted battery (fast charge first then trickle for hours). However if you deep discharge the battery too many times it can go bad and fail to recharge. Sounds like you are there now.

    But double check to be sure the off power drain is under ~200 mA with a charged 13 V battery
    Last edited by gc325is; 04-27-2018 at 12:01 PM.

  21. #21
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    Quote Originally Posted by gc325is View Post
    You should be using a battery charge. A dead battery is ~ 60 AH / 2 amp charger = ~ 30 hours on a battery charger

    If you use only the alternator that can be a problem, it charges until the battery voltage is up to ~13.5 V and with a dead battery you can get that false voltage with just a few amps of charge. ( plus you already got ...The diagnosis from that was an inadequate alternator. According to the manager there, it was just enough to keep the battery at its currently state. Pretty much saying, each time I start the car, it’ll drop in voltage. So eventually, it’ll drop so low the car won’t start.) You can also damage the alternator by over driving the circuits charging a dead battery.

    An intelligent battery charger will properly charge a depleted battery (fast charge first then trickle for hours). However if you deep discharge the battery too many times it can go bad and fail to recharge. Sounds like you are there now.
    I didn’t use the alternator to recharge the battery, the car won’t start at all. Like I said, I hooked up the battery to do a voltage test, and the battery drained completely almost instantly. I am using a charger to charge the battery. I will not be reinstalling the battery into the car again until I am certain it is fully charged.

    Once it is, I will disconnect the lead going to the alternator, and then run a draw test. That will eliminate the chance of the alternator causing a short in the circuit, which is a primary suspect to being the problem. If that test does not yield a conclusion that the alternator is solely the problem, I will look elsewhere.

  22. #22
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    your car might have more than one issue. Nevertheless, symptoms of a car dying while it was running and your charging system being unable to show a voltage reading higher than the base-line of your battery makes the alternator a big suspect. Pin-pointing the issue of why your battery goes near empty over-night might take some time. If you want to have a car running in the meantime, you may want to replace the alternator first.
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  23. #23
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    Quote Originally Posted by mnguyen84 View Post
    your car might have more than one issue. Nevertheless, symptoms of a car dying while it was running and your charging system being unable to show a voltage reading higher than the base-line of your battery makes the alternator a big suspect. Pin-pointing the issue of why your battery goes near empty over-night might take some time. If you want to have a car running in the meantime, you may want to replace the alternator first.
    That’s what I’m worried about. With the many number of grounds and connections throughout the car it could be anything. In the meantime I guess I’ll just have to daily the M3.

  24. #24
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    A bad ground, unless on the alternator, DOES NOT drain your battery. Think about it. INcreased resistance of power flowing to negative earth slows drain.

    (on the alternator it would affect the ability to charge so not an actual drain. Alternators only usually drain when a diode goes)
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  25. #25
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    Quote Originally Posted by E36328Coupe View Post
    A bad ground, unless on the alternator, DOES NOT drain your battery. Think about it. INcreased resistance of power flowing to negative earth slows drain.

    (on the alternator it would affect the ability to charge so not an actual drain. Alternators only usually drain when a diode goes)
    Noted. Electrical stuff has never been my strong suit. I’m just trying to think logically about this. What could possibly drain the battery so quickly? At least some electronics would work, wouldn’t they?

    Also would a positive lead grounded to the chassis cause this? Like say the battery wire leading to the front had an exposed section touching the body, would that drain the battery? I’m assuming it would because it would complete the circuit.

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