Question about 1985 BMW R 80

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Battery discharge in a week to 10 days

Bought this cycle used 2 years ago and have gone through two batteries. The last one due to cold weather,forgot to remove, old fart syndrome. Gauge indicates charging when driving bike, needle jumps between 10 and 13. When bike sits for a week or 10 days not enough battery power to turn over engine?????? completely mystified.

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  • BMW Master
  • 39,960 Answers

Hi, Tony first perform the following tests:
1. Fill acid type batteries to proper levels.
2. Charge battery overnight at 1-2 amps you need 12.5 volts or better after charging.
3. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
4. Hook up battery positive cable, then with your multimeter on the milliamp scale connect one lead to the negative battery post and the other lead to the ground cable. Meter should read 3 milliamps or less, 10 milliamps with a radio, 15 milliamps with radio and CB. If your meter reads higher you need to isolate the circuit by pulling fuses and circuit breakers one at a time and observe meter for a drop in amperage then get out your test light and track down the short in that circuit.
5. Hook up a voltmeter to the battery and start the engine, if meter falls below 9.0 volts while cranking you need to perform a proper load test on the battery and replace if necessary.
6. With the engine running at 3600 RPM, the battery should read 14.3-14.7 volts if not continue tests.
7. Unplug the voltage regulator from the alternator at crankcase by the front of the primary cover.
8. To test voltage regulator go to https://www.youtube.com/watch?v=F8EjV0IjW9Q
9. With ohm meter, one lead grounded, touch alternator pin meter should read infinity, if not replace the stator.
10. With ohm meter, both leads touching alternator pins meter should read 0.1 to 0.2 ohms on 1989 and later models. 0.2 to 0.4 ohms 1988 and earlier models, if not replace the stator.
11. With the voltmeter set on AC scale, both leads touching alternator pins meter should read 16 to 20 volts AC for every 1000 RPM'S 1989 and later and 19 to 26 volts AC for every 1000 RPMS. If not, replace the rotor.
For more information about your issue please visit the websites below. Good luck and have a nice day.
Stinkin R80 battery keeps going flat
http://forums.bmwmoa.org/showthread.php?62422-1986-BMW-R80-Charging-question
http://www.lamaneta.org/manuales/manuales/BMW%20R80GS-R100R%20Manual%20de%20Taller%20ingles%205555.pdf
BMW Motorcycle Parts Fiche OEM BMW Motorcycle Parts online 1970 present BMW
http://www.bmw-motorrad.com/us/en/index.html?content=http://www.bmw-motorrad.com/us/en/services/manuals/manuals_main.html¬rack=1

Posted on Jan 01, 2016

6 Suggested Answers

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Posted on Jan 02, 2017

Kimi
  • 277 Answers

SOURCE: bad battery

Don't rely on on whether the bike will start at a gas station to determine if the charging system is working. Get the multimeter out and do a proper test. Should be getting about 14.5 volts @ around 3K RPM. It's too easy of a test to to just skip. If it is charging then start looking for something else. Was the new battery properly charged to begin with? Loose battery connection? I suppose the GPS could be too much but you said that it was dying last november, so I would suspect something else. P.S. you need a properly charged battery to get an accurate reading for the charging test.

Posted on Nov 20, 2008

  • 2712 Answers

SOURCE: battery dead

If you don't have a multimeter, get one from Radio Shack or Wal-Mart. Measure the voltage across your battery while the bike is off. Then measure the voltage across the battery while you push the starter. Finally, measure the voltage across the battery with the bike running (if you can get it running). BTW, when jump starting a bike with a car, LEAVE THE CAR OFF.

Posted on Nov 20, 2008

SOURCE: New battery does not hold charge.

It sounds to me that the electrical system has a draw on it and is draining the battery. Have an electrician do voltage draw test on your system. You could on your own pull the negative bat. wire off and just barely touch it to the terminal and if you see or hear a spark then you do have some thing drawing on the system. Something left on or something stuck on in your system.Hope I have been of some help. donnyb60

Posted on Mar 21, 2009

  • 163 Answers

SOURCE: My 2006 BMW G650 has a brand new battery that died after 3 weeks

Sounds like you need to check your charging system.Battery when engine running alittle over idle should charge at 14.5 volts. If it does not check the output of your stator by testing lead at the regulator rectifier... It may be you have a bad regulator rectifier...

Posted on Sep 03, 2009

  • 8404 Answers

SOURCE: R1200 CL Battery problem

rectifier shorted to ground maybe?

Posted on Sep 07, 2009

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