[FrankenDesmo]

Curiosity got the better of me and I've just nipped out to the shed to check - charging holds steady at 14.32-14.33v all the way from idle to as far as I was willing to rev at a standstill (well over 4k, anyway). Battery is then sitting at just under 13v immediately after being shut off.

I think the charging voltage is OK - any higher would start to become a problem, yes? (EDIT: googling suggests the accepted range is 13.5-14.5, so yeah that's a good healthy charge).

The battery brand is Atom, and looking at the listings on ebay, they are certainly, erm, budget oriented. The seller did tell me it was just a cheapie when I got the bike, to be fair.

Is it possible the abuse it suffered through not being charged at all by the RR, then potentially over-charged by a dodgy chinese RR - I had an issue with that where the ignition fuse would blow above a certain rpm (around 7.5k from memory) - then left to sit for a few months in a cold shed, then hooked up to a healthy RR has left this cheap battery in a state where it just isn't happy?