Battery drain

Discussion in 'E46 M3 (2001-2006)' started by lambert, Oct 13, 2018 at 8:55 PM.

  1. 13 Oct 2018 at 8:55 PM #1
    lambert

    lambert Wearing official robes

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    Hi all.

    Along side my random threads recently which i thankyou all for your kind help I’ve been plagued by this nightmare battery drain my car appears to have.

    I bought it of a close friend about 5 weeks ago who owned it 12 years, he never used it much, it’s absolutely mint with no known issues/faults.

    The alternator is charging the vehicle we have now established that much.

    The car died whilst I’ll was working on it (just cleaning) over a period of a few days, i put it down to crap new buyers luck and off I went to coopers for a brand new bmw battery.

    Fast forward 2 and half weeks and I approach the car to find no life in the central locking, sadly the new battery’s dead.

    Before I chuck more money at possibilities do any of you clever cutters know of anything it may be?

    I had a weird feeling it maybe the Bluetooth as this was one of the last things I set up on the car before it stood for a few days, (it’s a factory device)

    She’s absolutely stock bar some eibachs so no hidden gimmicks or wireing anywhere.

    It’s got the usual bits, satnav/heated seats.H/k

    I’ve heard heat resistor (hedge hog) are a possible cause?

    Any help deeply appreciated and thanks in advance as always.

    Lambert
     
  2. 13 Oct 2018 at 9:24 PM #2
    scoosh89

    scoosh89 Achieved official socks

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    Do you have a multimeter?

    If so open the boot and lock the car, set your meter to mAmps.
    Put it across the battery and check what the car is drawing, it may take about 10-15mins for the car to go into to shutdown mode where all the modules fully shut down.

    Ideally you want it to be around 0.05mAmps or less.

    If it higher say 0.10+ then you have parasitic drain somewhere.

    To check your alternator put your meter in volts DC and put them across the battery or the battery posts under the bonnet and start the car. you should be getting around 13.8-14v.

    If your not getting up to 13.8v then your alternator is not outputting correctly.
     
  3. 13 Oct 2018 at 9:27 PM #3
    GolfDuck

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    The hedgehog is a common battery drain.
     
  4. 13 Oct 2018 at 10:06 PM #4
    Coops

    Coops Wearing official underwear

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    My battery drain turned out to be the BM54 Unit in the boot. You can pull the relevant fuse 41 (i think) when not using the car and see the problem goes away:thumbsup:
     

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