No answers yet, but just got off the phone with Byron at XS (Nathan's out on holiday). After a lengthy discussion on the history we agreed that the only way to really know for sure if this battery is right for the application or not is for them to do a full diagnostic check on it. It's heading their way in today's mail, so we should have an answer by weeks end. If it's a capacity issue then I'll be looking at reworking my trunk to tuck a bigger battery into the corner, or worst case moving the gas tank over a few inches to make room. Fingers crossed that my S680 is weak under load, and a new one will fix the problems.