I had a similar situation on my R18 FE a couple of weeks ago, which FYI also has a DataTool stealth tracker.
In the garage for a week since the previous ride, wheeled her out but the battery was flat. No movement on the speedo and nothing on the LCD display. I put the battery tender (BMW) on her overnight, and although she started up next day and I rode for an hour or so without mishap, I noticed the system had reset and that I was unable to set the time (kept going back to “12:00”) or the date (it wouldn’t let me input the days or the month) and I was getting a service warning for 5 months time that wouldn’t clear. The Dealer said it sounded like a battery problem and gave me a date 5 weeks hence to come in and have it looked at!
I went out for a ride a few days later (she was on the battery tender and started fine) and I stopped after an hour for a tea break. I used the reverse gear to reverse into a space to park and switched her off. A few minutes later, having decided to go somewhere else instead, the engine wouldn’t start, and when I turned the ignition off and then back on, I got nothing. Completely flat battery. I called BMW emergency assistance, who arrived within the hour, diagnosed a battery problem and jump started the bike. I rode home perplexed and put the battery tender on.
The following morning I started the bike up first time in my garage, and as a test reversed out about 10 metres onto my drive, turned her off, and then went to turn her back on. She was completely dead.
BMW emergency assistance recovered the bike the next day back to the Dealer and they diagnosed a faulty battery and swapped it out. Clock is reset, date is reset, no service warning, she starts, reverses, turns off, starts up again - just like she should. As UK_r18_Classic pointed out, having gone completely flat that first time, I think the battery was damaged and it simply wouldn’t hold a charge and using the reverse drained whatever charge there was.
By the way, the BMW Emergency Assistance call centre were first class and the first recovery technician did a great job getting me up and running on a bike he was totally unfamiliar with. The second technician on the other hand was wholly unimpressed with the bike (not worth £20k!), was always recovering BMW’s he said, and told me to get a Harley, like him!