Question: It's about about halfway through the winter storage period (I live in New York), and I’m wondering if I need to recharge my boat’s batteries.
I left them fully charged when I winterized the boat and covered it up for the winter, but I’m thinking I should check them again and see if they need to get another charge. Or is it just a waste of time and I can just leave them until spring?
Answer: It really depends on the way you left things on board. You don’t tell me whether you left the batteries connected or not. Also, if you did, what sort of equipment might you have on board that could contribute to what are referred to as "parasitic loads?"
If you completely charged your batteries and disconnected them from any loads on board when you stored the boat for the winter, your batteries are probably still in fine shape, assuming they were in good serviceable condition when you put the boat away.
Typically batteries in storage only lose about 2-5% of charge capacity per month to self-discharge, a completely normal function of all storage batteries. So considering the maximum here at 5% per month, a 5-month month lay-up period would leave the batteries at only a 75% state of charge.
Now, it is not recommended to leave a battery in a 75% charge for extended periods of time, as sulfation will begin to occur -- but as long as you get to spring commissioning early you should be OK as long as you fully recharge the batteries ASAP.
If you left your batteries connected when you put it away, I do recommend a mid-winter check and re-charge. Although the parasitic loads I’m discussing here -- things like radio and GPS memory and small LEDs used for system monitoring and the like -- only consume milliamps of electrical current, it is cumulative and surprising what the total parasitic loads can amount to on a modern boat.