This sudden battery drain reminds me about my brown K2 that suddenly had no power at all last spring.
My battery charger (CTEK MXS 5.0) reported battery failure.
No fuse gone. It has only one std plus hanging fuses for all 12 V from battery to all additional relays.
Quickly found that the ignition relay I had mounted had a shortcircuit between 12V and ground.
Charger happy when I removed the hanging fuse to it. Fuse OK.
Relay was not auto type that has some IP rating. I used mini relay for electronics.
Remembered that I washed the bike a week before....
Replaced relay just for sure, mounted it upside down closer to battery so no water could splash onto it as before. Tape and shrink hose helped too.
- So a small current leak can drain battery and not blowing the fuse.
This happened in my garage, correct place for failures.
I have had a battery issue on a vacation ride to Italy when headlight suddenly went black in the evening into a sharp corner on a small coastal road. Not nice surprise. All blinkers started to glow when headlight went black.
I had to keep rev over 4000rpm to have headlight.
This was not seen before on highways when rev was constantly higher.
That was a bad battery.
Cheap battery not much maintained with a charger.
Battery chargers first half of the 80's were not that good, almost DC thru its output.
I encountered drained battery on my car this morning
Car not much used the last year, not maintained with charger either. Alarm drain battery if not charged.
Alarm with its own battery was pissed when I had to open car with key manually plus open the hood for charger.
Back in business after a few hours charging, resynching key with car so remote works.
Charge it for 2 days every month is my plan.