I have had Deltran battery tenders for years. Bought one for my 81 4/4 in in 90s and bought several since for the rest of the fleet. Leave them on all the time. I even have one that I have run over. It looks like hell, all bent and crushed, but is seems to be only superficial damage and it works fine. I don't have any of the gel batteries or other high tech stuff so haven't gone to any of the newer battery conditioners.
Cheers,
