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Thread: Battery decharging 2002 M Roadster

  1. #1
    Join Date
    Oct 2009
    Location
    Excelsior, MN
    Posts
    12
    My Cars
    2001 M Coupe

    Battery decharging 2002 M Roadster

    Hi, return member after a few years absence. Installed new battery even though the old one wasn't too old. It wasn't holding a charge, and no obvious reason for it not holding a charge for more than a couple days (has't been driven much for the past year). Salesperson told me that there may be a computer reset needed to regulate the recharge rate of the battery by the car, old vs new battery. Does this sound familiar to anyone?
    Thanks, and nice to be back!

  2. #2
    Join Date
    Dec 2013
    Location
    Chicagoland area
    Posts
    4,372
    My Cars
    EXOTICS
    Newer gen vehicles-yes-require battery reset,
    your vehicle-no-not required.
    Test your vehicles electrical system for parasitic drain.
    Last edited by MIKYZZ4; 07-11-2018 at 07:34 PM.

  3. #3
    Join Date
    Oct 2009
    Location
    Excelsior, MN
    Posts
    12
    My Cars
    2001 M Coupe
    Thanks. Suggestions on testing for drain?

  4. #4
    Join Date
    May 2002
    Location
    SW Florida
    Posts
    12,681
    My Cars
    99-01 M Cpe & Rdts, X5M
    An easy test is to put an ammeter in series with the battery connection and start pulling fuses, that may help in narrowing down in which circuit the fault lies.

  5. #5
    Join Date
    Dec 2013
    Location
    Chicagoland area
    Posts
    4,372
    My Cars
    EXOTICS
    here is an informative video:https://www.youtube.com/watch?v=QRso1A0VScw

  6. #6
    Join Date
    Mar 2004
    Location
    San Diego
    Posts
    3,489
    My Cars
    2000 Z3 2.3, 2014 M235i
    I had a parisitic drain for a while, it took some time to figure out it was the trunk interior light staying on.

    That one is easy to isolate first, feel if the light is warm after the trunk was closed, or can leave your phone in the trunk filming...

    If thats not the issue at least you can easily eliminate it.

  7. #7
    Join Date
    Aug 2012
    Location
    Newport UK
    Posts
    48
    My Cars
    1999 z3 1.8
    Check what the alternator is putting out, I had an alternator that was only putting out 12v and after a night run using headlights the battery was flat next day. Put a new alternator in and charge restored to 14v. Put a voltmeter across battery terminals and run the engine to check the output its getting. You should see in excess of 14v if its ok.

  8. #8
    Join Date
    May 2015
    Location
    savannah, ga
    Posts
    93
    My Cars
    2000 m roadster
    Another thing to check is the main terminal under the hood on the passenger side of the vehicle. I had loss and couldn't figure out why. I put in a brand new alternator and still had it. Then one day I was checking something under the hood and noticed smoke coming from that terminal. It was so hot it was starting to melt the plastic around it. It had become corroded and wasn't making connection all the time. I sanded all the corrosion off and put it back together and everything worked good after that.

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