Guess what's sitting in my garage? My '06 BMW R-1200RT with a dead battery. I will replace it this weekend - but here's the deal, BMW is using a poorly constructed battery in these bikes; Going back the battery in it's predecessor a R-1100R was always a weak sister, slow cranking and on that bike the ABS would come up with an error right after a cold start. Alternator fine. Battery load test would show 8 volts when under a load. Just barely passing. I replaced it with another BMW by Excide battery - it was better but also a weak performer. After 6 months all the issues returned. A trip to the dealer and warranty replacement - same issue. I fineally grafted an Interstate brand UPS battery into the bike and WOW! Fast cranking, voltage stays at 11 volts when tested and the ABS never came up in fault mode.
Much batter - that battery worked until I upgraded the entire motorcycle. Now I am back to the same old crap with the new bike. The motorcycle is still under warranty -so I will replace the battery with the official BMW battery. But once the warranty os out I will try to find a suitable AGM

So, I would assume that the battery is the issue.