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What's running down the battery ??

Discussion in 'Technical Q&A' started by peajay, Feb 8, 2004.

  1. peajay

    peajay Formula Junior

    Apr 17, 2002
    454
    near Paris, France
    Full Name:
    Paul
    I haven't started up my 328 for about 6 weeks over Winter and was quite surprised to find the battery almost flat. I replaced the battery last September so I am certain there is no problem there. I didn't bother to use the battery shut off switch this time. What do you reckon is causing the battery to run down ? I have had other cars unused for longer than this in the past with no problem.
    The battery is already on charge so no big deal, but I am just curious.
     
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  3. ShanB

    ShanB Formula Junior

    Jul 9, 2003
    547
    Tejas/Europe/Desert
    Full Name:
    shanb
    The usual culprits - alarm system when left on for weeks at a time, glove box lights, underhood lights (don't remember if the 328 has any), and the courtesy lights inside the door. Other than that, I'd switch to an Optima battery. Let us know what you find.
     
  4. MarkCollins

    MarkCollins F1 Rookie
    Owner

    Jul 2, 2002
    3,201
    South England
    Full Name:
    Mark Collins
    Alarm/ Immobilisor? Clock?
     
  5. Mule

    Mule F1 Rookie
    Rossa Subscribed Owner

    Jun 25, 2003
    3,559
    Alaska
    Full Name:
    Mule
    An Optima battery wont solve the "problem", maybe just give you more time before it is dead. The battery will run down after a few months if not used. Mine did it in 8 weeks with a brand new Optima. I blame the clock, the alarm, and cold weather.

    Same battery in my truck has gone four months and still started. Same weather, alarm and clock in the truck.

    Disconnect the battery, trickle charger (lots of threads) or start it up every now and then (but look at the threads on how long to run the car to charge the battery, dry out the exhaust, circulate the fluids, etc.)
     
  6. sduke

    sduke Formula Junior

    Mar 10, 2003
    825
    The Hub City, Texas
    Full Name:
    Steven D
    If you want to check the amp draw on the system there is a simple test.

    After fully charging the battery, disconnect the positive terminal. Connect the negative lead from your volt/amp/ohm meter (set in the 1-3amp mode)to the battery and the positive lead to the disconnected end of your positive battery cable. If your reading is above .05 amps you have an excessive draw. If you have an excessive draw, the best course of action is to begin removing fuses one at a time and see if the draw goes away. If it does not go away after removing all the fuses, disconnect the main alternator lead and check the results. The alternator is a common point for discharge.

    All cars have some draw. There is even a draw across the top of your battery. All batteries will eventually discharge completely. Six weeks does not seem excessive. Newer cars with multiple computers will run batteries down much faster due to the computer memory that must be maintained.

    Hope this info is helpful
     
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  8. Cincy Ken

    Cincy Ken Karting

    Jan 24, 2004
    219
    Cincinnati
    The battery on my 1989 328 GTS also runs down when the car is left unrun for a little over a week. One week hasn't been a problem, but 11 days is too long. In contrast, when the battery had been disconnected for 6 weeks, the car started right up after reconnection.

    The prior owner was somewhat concerned about this, and either kept the trickle charger on, or disconnected the battery when not in use. Both he and his mechanic attributed this to the analog clock, although I've not heard any confirmation that this has been positively identifed as the source of current drain. I've also heard that a clock rebuild might help, but, as the clock keeps good time, I've chosen not to pursue this.

    I've noticed trickle chargers on other 308/328s, so I assume battery drain is a common problem. The trickle charger is an easy solution, with the disconnect being a good alternative when the vehicle won't be run for extended periods, as long as you're willing to reset the clock, radio stations, etc.
     

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