Kept mine on a tender too and it fired right up in spring, so I have to disagree with blaming the tender. A tender only keeps the battery topped off, it can't fix a battery that was already weak or old when you parked it. Cold can also do a number on a battery that was on its last legs, and sitting for months lets gas go bad and lets other stuff dry out. Next time get the battery tested before winter and toss some fuel stabilizer in the tank, that combo works way better than the tender by itself.