R80 battery not charging
 

Hi folks,

A strange thing - the battery red light on the instrument panel goes out with increased revs, suggesting the charging system is working fine, yet a multimeter reading stays at 12.75 V when it should be going up to around 13.5 V.

Could this be because the gel battery is on its way out? It's 4 years old and recently plummeted to 12 V. I had left the bike unused for 3mths, battery disconnected, having not used it much the preceding 2 mths.

I got it charged up to 12.75 V, but as mentioned above, it doesn't appear to be recharging via the alternator.

I have read that once gel batteries have been allowed to go dead, they're hard to resurrect.

Thoughts?

If so, can I stick any old 12 V moto battery in it, assuming it fits (I'm currently in Mexico), or does it have to be BMW?

Cheers,

Bob

You can use any 12V battery that fits the battery tray although I have had a gel battery last years with gaps of 6 months between use, they are much more resiliant than lead/acid ones.
The charge light going out suggests all is well and I suggest borrowing a good battery to carry as a backup and taking the bike for a ride with the lights on to see what happens, if it keeps going all is well.
A quick check is to look at the alternator brushes and see if they are not worn out, they are shot when about half worn down so might look ok and will give some charge but it will quick drop off, also clean the slip rings on the rotor.

One test ... remove the voltage regulator and short the Df and D+ wires in hte voltage regulator socket - there are 3 connections .. the brown wire (ground) you leave open, just short (connect together) the other 2.
This should set the alternator to maximum charge ... start the engine an rev it while watching the battery voltage .. if the voltage rises then the voltage regulator is suspect. Otherwise ... something else is wrong. Do not continue to run the bike this way - the battery will be over charged and eventually die, but for a short term test it is fine.

Oh .. when you remove the front engine cover ... you are disconnecting the battery before you do it .. otherwise you can short out the diode board and blow it up.

Thanks, Mark and Warin. You're stars. I'll give all that a go.

Anon!

Not quite sure what did the trick, but the battery is now charging with revs (around 13.75 V).

I checked the bushes, which though still working need renewing soon (close to half worn). Checked the rotar for a closed circuit - only 0.05 resistance which I take to be fine. Cleaned the slip rings with petrol.

Then connected the blue and blue/black wire in the regulator 3-pin plug. Started the engine. With revs the multimeter read > 14 V.

Thinking it must be the regulator at fault, I plugged it back in, started the engine, revved and, lo and behold, the meter reader 13.75.

Must the gremlins up to their mischief again.

Will take for a spin with lights on tomorrow morning to escape the town before the traffic.

Thanks again and all the best!

Bob

Check the connectors ... you have disturbed them and remade the connections ... one of them is probably 'dirty' or loose. Bit of a clean and re crimp things so they are good and tight just might remove the fault.
Good Luck.

Makes sense. Cheers, Warin.