[Bobcat]

Charles ... when I was traveling heavily , I used to leave my truck in the garage for a week or two at a time without starting it ( had a company car ) and never had any battery problems . Then I started having some cranking problems and finally a dead battery . Started leaving it on a Battery Tender when I was gone , but had to replace it after a little over 2 years . Long story short .... the new cars today always have a small drain due to all the computer/electronic circuits etc ( theft alarms etc ) to let them keep their presets etc, according to the tech at the Ford dealer . Could that be what is happening and it becomes more of a factor in colder weather as your battery ages ?
As a battery ages , the plates sulfate up some . When it isn`t being kept full charge , that means the plates will sulfate that more quickly and then the battery won`t take a charge like it used to do and it goes downhill even quicker . I have a battery in my Galaxie that is a replica of an old tar top and has been kept on a Battery Tender its whole life and it`s almost 7 years old now ..... hope I didn`t just jinx myself . Why you didn`t have a problem with the 5 year old one , I don`t know .

Bob