I put all my batteries onto a multi stage charger for 8-24 hours every couple of weeks regardless of use. I know a lot of people say multi stage charges or DC-DC charges do nothing and an alternator is all you need to keep them charged but I know I get on average nearly 10 years from a battery and a lot only get 5-7, some even less.
In my opinion using a multi stage charger is the only way to get max life and a reliable use . I am no expert but assume its from the trickle charge that constantly keeps them at 100% full

