I use a Battery Tender on 4 of my 5 vehicles; the ones that do not get regular use. As stephenm correctly notes, above, a Battery Tender monitors a battery's state of charge and only adds charge if battery falls below a certain voltage. My Odyssey battery was a few years old in 2011, when I got the 03 Stone Touring it was in, and it still is working fine. I load test it every six months, just to be sure.
Ralph