I can guarantee this has been posted before....but it was news to me. I found my battery was dead yesterday because I left the key on. So I threw my battery tender on it thinking it would charge overnight....wrong. A battery tender will not charge a dead battery. The battery has to have SOME voltage to trigger a diode for it to charge. I ended up having to jump start it and ride it a little...then put the tender on it. Now all is good. Lesson learned.