I charge them when I put the boat away and maybe once or 2x over the winter if there's no snow on the cover. Then before re-commissioning I charge them again.
I'll plug in my charger when I open the boat (once the batteries are connected that is). I'm probably due for a deep cycle as I replaced the starting battery last year. **(2) batts onboard.
I keep my winter stored flooded lead acid batteries hooked up during the winter off season on maintainers. The starting batteries don't like to get fully drained to often. My motorcycle battery is 6+ years old and still doing fine.
I trickle charge mine a couple of times over the winter.
But, if it's a good battery that is fully charged they can have a full charge without charging.
Helped a friend get his boat ready last week.
He left his 3 year old battery in all winter with the boat outside.
We had about a month of -22F weather and 2 months of -15F I believe.
Put battery on charger and charger said full after 10 minutes.
I tested it and it had more than rated CCA's.
My batteries self discharge about 10% every month. My regimen is to recharge monthly all Winter. When I put them back in service they are 100%.
When I take them put of service in the fall, they are usually about 95%. If I disconnected them in the Fall and they were at 80%, I would have charged them up immediately. If I didn't I am quite sure I would have a problem now.
Good luck...
(PS - I typically get about 8 years out of a quality battery)
year 6 on my battery. Charge late fall, disconnect, put winter cover on and forget about it. Top off in spring, go boating. We also get to -40 at times here.
