I have this one that I got at o'reilly. I have one on 6 different cars. Never had one of these go bad but can't say that about others. Wired it with a permanent connection to the posts in the engine compartment and ran the line back by the door so it gets plugged in at that location when it's not being used. My battery was always low without a battery tender.
1997 GTS(Bone Stock), 1963 Corvette coupe red, 1963 blue corvette coupe, 1987 Buick Grand National