Thanks - charged up the battery last night and it's holding charge @13.3V so looks plenty healthy enough - @Mississippi Bullfrog will try measuring with the bike running. Took it to the garage this morning and they said the charging circuit was A-OK, possibly a faulty third-party USB charger (switched) was draining the battery in the meantime. And yep, headlight's on all the time on this bike so maybe that's draining the battery while doing all this current super-slow riding. Guess I'll just have to keep an eye on the battery over the next week or so and not stray too far from home until I'm confident it's OK. I'm a learner and this bike's been 100% reliable since buying last year - not a great feeling riding a bike you're worried might junk out at any time - on the bright side, at least I know how to jump start the thing now! Thanks again.