2004 R1200GS Battery Draining

[celticbeemer]

Hello All

I thought i had a dodgy battery, as after sitting up for a while the bike would not start, i charged the battery, it started but a few days later it would not start again.

So i bought a new Yusa Battery, and all was ok for a week or so, then same thing again.

I am assuming that the battery is good, and therefore started a search about this problem. the most common fault is a failed Alternator Rectifier.

Can anyone tell me how to locate and replace this. (Some pics would be very helpful.

Regards
CelticBeemer

[marc]

Where did you find info about alternator rectifier issues on a R1200GS?

The alternator is a single assembly. If any part of it fails the entire alternator is replaced. But before you do that....

Is the battery dying with the bike being used, or just sitting? If just sitting have you measured the ignition off battery draw? Most folks report 4-6 ma with the ignition off. Have you measured the voltage at the battery with the bike running? Should be a bit over 14 volts. If you have a GS-911 you can also capture the real time battery voltage as reported by engine management.



That's the output from the alternator as reported by the bike. The large drop is when the bike was being started.

If you do have to change the alternator I'd look for a used unit. I don't think a late model alternator won't match up to your bike without some wiring modifications.

[celticbeemer]

Hi Marc, thanks for your reply. i googled BWM R1200 GS Battery Drain, and several sites referenced an issue with a Alternator Rectifer (and not just BMW).

I have a GS911 and will hook it up tomorrow.

The alternator would seem to be charging ok, as the bike will start all day after the initial recharge.

I used it today and stoped and started it several times, and there was no issue

What else could be wrong.

Cheers
David

[marc]

You need to measure the key off current draw by disconnecting the battery and hooking an ammeter in series. Do NOT start the bike with the ammeter connected.

I'd expect to see about 5 ma plus or minus a few ma draw. If you are seeing much more you've got some device pulling more than it should or a partial short to ground somewhere in the wiring. A draw of 150 ma, for example, would drain your 12 AH battery in about 80 hours.