Dead Battery

[EvMachina]

My 79 R100S showed the generator light while at idle yesterday. Today it started this morning but later in the day I had to push start it as the battery wasn't giving enough to turn the starter. I'm using an Odyssey drycell battery that so far has been great.

I'm reading through the forums a bit does this sound like a Voltage regulator? any ideas would help. Thanks

[20774]

Generator light at idle, especially a low RPM, seems fairly normal.

First things first...attempt to recharge the battery with a separate trickle charger. Then start some testing. Put a multimeter across the battery and watch the voltage as you attempt to start the bike. Shouldn't fall below 10-10.5 volts. You could also consider taking the battery to a car parts store and asking them to load test the battery. It may be that you need a new battery. How old is the current one?

If you can start the bike, you need to monitor the voltage across the battery. See what it reads at idle...likely around 12.5-13 volts. Increase RPMs to above 3K. Voltage should read close to 14v. If not, then you'll need to do more troubleshooting.

It could be the voltage regulator...maybe not. Could be the alternator rotor. Could be the brushes. Could be the diode board.

Start with the basics and work from there. There have been other posts on exactly this subject. Try searching... Also, Rick at Motorrad Elektrik sells a nice troubleshooting book. It's worth the cost (maybe $25) and is a must to take with you on any long trips.