I took the RC out yesterday morning for a dose of twisties. The bike hadn't been fired up for a couple of weeks, but cranked, started, and ran fine. I was a little short on petrol, so I stopped at a station in the closest town (around 15 miles from home) for some. After the fillup, the battery allowed me just two feeble grunts, and then nothing, deader than tin. Fortunately, my stop was near the top of a nice, long hill, so I was able to bump start and make it back home. After the ride home, the bike restarted without a problem. Fifteen minutes on the Battery Tender, and the indicator said charged.

Any theories? None of it fits my experience with weak or dying batteries. After that first start, the ride to town (which was spirited, hitting triple digits a couple of times) should have charged the battery further rather than pulling it down.

My guess would be regulator/rectifier.

My guess would be regulator/rectifier.

Agreed.
Throw a meter across the battery posts and hold the engine at around 4000 revs. You should be getting around 14-14.5V.

Yup. May also have a bad cell in the battery. The rectifier is going to be throwing some crazy high numbers so test after the regulator... Like he said about 14 1/2 volts.

Marco427 - can you tell me how you fixed this? I have the exact same problem. I only get one chance to turn the starter and it sometimes even cuts out on me when I pull the clutch in after engine braking... But I don't always experience the issue i.e. the battery appears to operate at full power sometimes.

Some of the material out there suggests it could be a bad ground or not enough spark coming through the plugs.

Let us know what you found!

Marco427 - can you tell me how you fixed this? I have the exact same problem. I only get one chance to turn the starter and it sometimes even cuts out on me when I pull the clutch in after engine braking... But I don't always experience the issue i.e. the battery appears to operate at full power sometimes.

Some of the material out there suggests it could be a bad ground or not enough spark coming through the plugs.

Let us know what you found!

This is a regulator/rectifier issue. My bike did the same thing. It would do it sometimes and others it wouldn't, what I think happens (and this was the issue with my bike) is that after you are out riding for a bit the regulator starts over charging the battery and starts to kill it. If I pop started it and just sat there with the bike and rev'd it to 4.5k it would look normal on a volt meter, the only why they could tell on mine is they bolted the volt meter to the battery and went out and rode it. They said after a bit of riding it started throwing 17.5 volts on my battery and it would go up if you hit the brakes or something.

I replaced the regulator and it fixed this problem, now I'm having other issues but that was the cure to this specific issue.

If you can bolt a volt meter on the battery and secure it somewhere you can see it then go out for a ride and see what happens.