I've taken the battery out and hooked it up to the charger (and the charger certainly seems to agree that the battery needs charging), but this is ridiculous -- the battery was new only a month or two ago. I know it's not the dynamo this time, because the dynamo light has been on all the time when it should be (I've been watching it carefully); so that means something is hoovering up the battery charge, and I need to find out what.
All suggestions gratefully received...
Update: Okay, I'm stupid.