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Thread: R100 kills batteries

  1. #1
    Motorcyclist patiodadio's Avatar
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    R100 kills batteries

    My 1988 R100 RT just started draining batteries. The battery I had in it went dead so I got a new one. The next day that one was dead, I thought I might have got a bad battery so I got another one. The second battery was dead the next day. Got any ideas where to start looking ?
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    Registered User toooldtocare's Avatar
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    If you have an amp meter, disconnect one lead of the battery and put the meter in series with it. (you need a charged battery) Measure the "dark" current first, normally around 10 to 40 ma. If it is higher than you have an excessive load draining the battery. Because it goes dead over night, I bet the load will be closer to 1/2 amp, or so. If it isn't, but instead the lower values in the ma range, you got another bad battery. (The dark current is the normal load that electronics puts on a battery even when turned off.)

    Since you only have two fuses, disconnecting them will only eliminate 1/2 of the circuit at a time, not much help. Instead, unhook one thing at a time, starting with the easy things such as the clock (if it is an RT or RS), any accessories you installed, relays under the tank. If the meter does not return to the normal low reading, go inside the front cover (after disconnecting the meter first and leaving the battery lead off too). Once the front cover is off start removing more stuff with the meter hooked up again, the diode board, bean can, etc.

    Since there are several things that can cause a load like this, you do not have many other methods to find the "short." Of course, once you find the load you have to determine what made it go bad, old age, wires rubbing together, etc.

    Good luck.

    Wayne

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    R100GS, '89 Guenther's Avatar
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    Unless you have installed some new electric gadget recently I doubt that there is something draining the battery just like that.

    What is the symptom of your dead batteries? What does it measure across the poles when "dead"?

    When you put a new one in, does the headlight work, does it start?

    /Guenther

  4. #4
    Motorcyclist patiodadio's Avatar
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    Quote Originally Posted by Guenther View Post
    Unless you have installed some new electric gadget recently I doubt that there is something draining the battery just like that.

    What is the symptom of your dead batteries? What does it measure across the poles when "dead"?

    When you put a new one in, does the headlight work, does it start?

    /Guenther
    When I put a new battery in it starts great.



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  5. #5
    Nutfarm
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    Is it charging? If it's not you may have have a bad diode.

  6. #6
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by 47512 View Post
    Is it charging? If it's not you may have have a bad diode.
    How would that explain the battery discharging in less than 24 hours ?

    patiodadio after you put the new battery in were you riding the bike? If so how long?
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  7. #7
    R100GS, '89 Guenther's Avatar
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    patiodadio,

    arm yourself with a 10 Amp fused ampmeter and follow Wayne's suggestions above.

    Some wild guessing:

    If there is a short it would have either burned a fuse or melt a wire (with some smoke). But it would do this only once...haha.

    If the ignition key has a contact problem you would see maybe a light bulb still on; maybe dimmed.

    Maybe there is some gadget connected directly to the battery (bypassing the ignition key)? Check what else is hooked up to the battery poles.

    It would help to get some idea if you could measure the amps - between battery minus and the disconnected ground wire - with ignition off.

    Good luck!

    /Guenther

  8. #8
    Motorcyclist patiodadio's Avatar
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    Quote Originally Posted by happy wanderer View Post
    How would that explain the battery discharging in less than 24 hours ?

    patiodadio after you put the new battery in were you riding the bike? If so how long?
    Only started it and warmed it up, did not ride it. But it starts great with a new / fresh battery.
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  9. #9
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by patiodadio View Post
    Only started it and warmed it up, did not ride it. But it starts great with a new / fresh battery.
    Then something is pulling a fair amount of current. Follow Guenther's instructions and from your findings some insight may come. Depending on how much current is being drawn the next steps would be to start disconnecting some things one at a time to find the culprit.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  10. #10
    daven81gs daven81gs's Avatar
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    Thanks for all the info. I think I have a similar problem with an 03 I just bought. The owner said the battery might be a problem cause he "just wasn't riding it enough". He also complained that the clock ran all the time( yes!) so I think he was hinting that I might have a future problem. And I did. Got it home and unloaded it. Click click click. I've charged it and put about 150 miles about 8 short rides and so far so good.

    When I got a new tire I had the shop check the system and the batt was marginally low and charging was good but when I rode it home I noticed the clock quit working? The shop did poke and prod a lot of areas maybe the clock got shorted out?

  11. #11
    Registered User donbmw's Avatar
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    Have not had new battery go dead that quick. But every time I had the same problem it has been the diode board. Even though it was charging. If I was riding almost daily did see a problem until I was not riding for a couple days.
    1975 R90/6, 1980 and 1982 R65, !959 TR3A Triumph Car

  12. #12
    daven81gs daven81gs's Avatar
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    Thanks

  13. #13
    Motorcyclist patiodadio's Avatar
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    Quote Originally Posted by donbmw View Post
    Have not had new battery go dead that quick. But every time I had the same problem it has been the diode board. Even though it was charging. If I was riding almost daily did see a problem until I was not riding for a couple days.
    As you might have guessed, I not much of an electrician. How do I check the diode board ?



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    Registered User toooldtocare's Avatar
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    Quote Originally Posted by patiodadio View Post
    As you might have guessed, I not much of an electrician. How do I check the diode board ?
    Read here, just takes a bit of time and a DVM. http://bmwmotorcycletech.info/diodebds&grdgwires.htm

  15. #15
    Motorcyclist patiodadio's Avatar
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    Quote Originally Posted by toooldtocare View Post
    Read here, just takes a bit of time and a DVM. http://bmwmotorcycletech.info/diodebds&grdgwires.htm
    Thanks !
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