[tubman]

I have also had a battery tender go bad. It happened on a boat battery several years ago and did the same thing. I believe it was a "Schauer". I contacted the manufacturer and they sent me a new one and told me just to throw the old one away. Ever since then, I have been wary of battery tenders, as you have know way to tell if they're bad or not. What I do these days when I want to leave batteries on tenders all winter is to plug them into a cheap timer, available at K-Mart, Wal Mart, etc. I set the timers to go on 15 minutes a day. That way, the batteries get charged without the chance of boiling one because of a bad maintainer.