Battery not charging

[relliott]

The battery warning light came on during the commute yesterday so I came straight home. I pulled the battery and it looks original, so 5 years old and 42k miles. I bought a new battery from bulbs and batteries, charged and installed it. Now, the volts on the dash is staying at 12.2 even when running. Where do I start to figure this out? I rely heavily on the bike as daily transport so any and all input is appreciated. 2014 RT with 42k miles. Thank you!
Rob

[Genen8kua]

Do you have a digital multimeter? If not, buy or borrow one; it doesn't need to be expensive and is a good all-around electrical troubleshooting tool.

My first step would be to measure the voltage at the battery. If it's above 12.4 volts or so, it's fully charged, but if not, you might want to charge it again before going further. Then start the bike and see what reading you get. Your charging system should provide a reading of about 13.8 VDC at the battery at idle and then increase to 14.4 or so with higher rpm. If it doesn't do that, then there's a problem with your charging system.

It could be as simple as a poor ground connection somewhere, which can be madding to track down but simple to fix. Disconnect the negative (ground, black) wire from the battery and trace it to wherever it's connected to something (starter, etc.) and look for corrosion. Disassemble, clean and use a light coating of dielectric grease when you reassemble. You might even take that multimeter, set it to measure resistance and measure the resistance between the lug at the battery end (not connected to the battery) and a piece of bare metal on the bike (the engine's a good start). The resistance should be pretty close to zero. Even a couple ohms of resistance could cause enough voltage drop for that low reading on the bike's computer.

That's where I'd start. After the easy stuff, you can start trying to figure out alternator vs regulator issues, or take it to a shop if you're not comfortable getting into it further. I just found a nice writeup of a charging system check here

Hope you solve it easily!

Regards,

Gene

[relliott]

Gene, thank you, battery is at 13.1 volts just sitting there, goes to 12.5 volts at idle, and at 3k rpm only gets to 12.7 volts. Hopefully Jim will jump in here with some suggestions.

[Max]

I know I am being stupid but you measured 12V when you run on idle or with throttle? Because Volts go up only when your motor is revved up. If you have no lights on dash that are red, it charges normally. Only issue could be alternator belt but it runs for 35 k miles at least. Again, if it broke, you would have red light on dash.

[Shane R1100GS]

This is a water cooled RT right.

It could be the voltage regulator. They cost around $240.00. https://www.bobsbmw.com/store/microfiche/BrowseParts.aspx?GroupName=Engine+Electrics+(12)&MBike=56210&GroupID=12

If it's the generator it's around $3000 to $4000 job by BMW. The motor has to come out to replace.

Diagnostic thread on a gs over on advrider. https://advrider.com/f/threads/needed-diagnostic-procedures-for-r1200gs-lc-alternator-and-vintage-regulator-rectifier.1119480/