Im using both the tiny battery tender (wall wart style) and the smallest genius one (I store my bike and my wife's convertible every winter) had good luck with both of them. the battery tender was more expensive (the genius ones go on sale at ctc every once and a while). I like the genius better, the lights are more informative, and does 6V too (not that I have anything 6V to charge). I think both came with both clips and ring terminal options. I had a cheaper one from napa, it might have lasted about a winter and a half before it just quit.