I'd put a new battery in my wife's Lx150, kept it on battery tender intermittently through the winter, rode it 5 miles to work much of the summer with my GTS out of the picture....and on trying to start it after some work, it would barely turn over, and didn't respond to external charging.
I know it's possible for a battery to give up early, which may be the case, but wondering if there may be something else afoot that I should be checking for?