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Thread: Charging system - any battery experts out there?

  1. #1
    Join Date
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    Charging system - any battery experts out there?

    My wife drove home in our e46 last week, and the battery light was on, plus all the other lights starting coming on. Fortunately she got the car home and in the garage. At first I thought it was a bad alternator, it sounded just the experience several other e46 owners have had. However, I see the voltage over 14 with the engine running, and actually had the alternator and the battery tested at O'reilly. The alternator passed the test. I had the battery tested twice, once on the small machine, once on the big machine. It passed both tests.

    I think the battery is old, it has a sticker on it that says 11/09, so I'm assuming it is from Nov 2009, which is really old! Is it possible that it's testing good but it isn't really good? I notice that the battery light is staying on a bit when I start the car, but the car is still running and driving, I have not experienced the issue my wife did. Has anyone run into this before where battery passes the load test but is still bad? Is there anything else I should test before laying down the cash for a new battery?
    Euro '85 635csi E24, '03 E46 325xi wagon 5-speed, '05 325xi sedan 5-speed, '67 VW Bug, '14 F150, '17 Jetta
    http://sites.google.com/site/eurobmw635csi/


  2. #2
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    west chicago il
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    01 E46 330i 5sp man spor
    You most likely need an alternator also. Check battery voltage with the engine running. Should be 13.5-14.5v.

    Sent from my SAMSUNG-SM-G870A using Tapatalk

  3. #3
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    The voltage has been over 14V with the engine running, but yesterday the battery light stayed on for my whole drive home (15 min drive). I left the car running and measured the voltage when I got home. I had about 12.4V, shut the car off and had 12.4V. So I think I have an intermittent alternator, it definitely wasn't charging on the way home.
    Euro '85 635csi E24, '03 E46 325xi wagon 5-speed, '05 325xi sedan 5-speed, '67 VW Bug, '14 F150, '17 Jetta
    http://sites.google.com/site/eurobmw635csi/


  4. #4
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    Don't play, if the battery is that old, the likelihood is that it's dying. Buy a new one, cheaper and more convenient than a tow.
    I kept a battery alive for 8 years once, but used to remove and charge it over a full weekend every Spring & Fall.
    -- The more you study Politics, the more you realize that each Party is worse than the other one.- Mark Twain

  5. #5
    Join Date
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    Newburyport ma
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    88,m5 95 740 04 XI E90
    Battery light means there is an alt problem. Most likely a bad voltage regulator. These voltage regs can come and go.

  6. #6
    Join Date
    Aug 2010
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    325e 535i M5 325iT 330i
    Intermittent red light indicates flaky alternator. At that age, it is likely worn-out brushes and slip rings. Unless you are exceptionally handy and a glutton for punishment, best to buy a rebuilt unit.

  7. #7
    Join Date
    Mar 2017
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    Norwich, Connecticut.
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    E46 wag. E36 convertible
    Quote Originally Posted by Jackson42 View Post
    Intermittent red light indicates flaky alternator. At that age, it is likely worn-out brushes and slip rings. Unless you are exceptionally handy and a glutton for punishment, best to buy a rebuilt unit.
    Ok..Batteries can live from 0 to 12 years...5-6 years is more common. A new battery requires less attention from the alternator...in order to remain sufficiently charged to do it's duty. Older batteries, 4 to 6 years, require more attention from the alternator for recharge. Alternators also too have a limited expected life span.

  8. #8
    Join Date
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    2018 BMW M240i
    Be advised that BMW sourced alternators from Bosch and from Valeo. They are not interchangeable. The only way to tell which is in your car is to remove the air cleaner box and the upper hose, and use a flashlight and a mirror to read the label at the back.

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