I work at a tech college. We store a number of training vehicles in a pole barn for extended periods of time. Got tired of the batts going dead so we put battery tenders(not sure of exact brand) on them. Fire inspector came through and said . Told us they get lots of calls regarding those and fire risk. We took them all off(had to). On my old muscle I just disconnect the batt( don't even take it out)and reconnect in the spring when I get it back out.Been doing that for many years and I'm in WI. Cars live in an uninsulated/unheated garage and -20f happens here....current batt is over 10 years old. On my newer toy I just fire it up every month or 2....hate disconnecting the batt on new stuff....computers and all.