Battery not charging?

[Gaulois]

Yesterday morning I couldn't ride to work as the bike (07 1200gs) wouldn't start. The battery didn't have enough juice to turn the engine over. I assumed it was due to a cool night and when I got back yesterday afternon I tried again and it started up straight away. Rode around for an hour or so and left it.

Today I started it after lunch (no work today) and ran a few errands. Stoped at the local garage to pick up some milk and, once again, it wouldn't turn over.

It's at least 17c outside so there's no way it can be due to temperature. What's odd is that no warning lights have come on even though the battery isn't charging.

I'm calling MBW Assist out but does anyone have any ideas as to what the problem is apart from an inadequate OEM battery?

 

[Fanum]

That (most likely) or slipping/broken belt, poor earth or faulty alternator.

Stick a multimeter set to 20v across the terminals of the battery and see what reading you get when the bike is turned off (should be a bit over 12v) then see what it says when turning it on (might drop to <9v) and what it registers when bike running at FAST idle (13-14 volts)

If charging ok (last option) and battery drops very low when turning over to start, it's the battery. (known weakness on 12's)

If reading is under 12 volts when turned off, battery is flat(ter than it should be) but not necessarily dead......

 

[Gaulois]

Thanks Fanum, it was the battery. BMW replacing it this am