I live in the Northeast as well and I have always done the following, which works for me:
I take the battery out of the boat and charge it overnight. Then I bring it into the basement and store it on a workbench. In the spring I charge it again and re-install it. I've been told to never store it on the concrete floor. I've also been told that really cold temps will destroy a battery. My basement usually stays in the 50's. I've had the same battery now for about six years and it is still mint, even though I'm sure some would say to replace it. Here are the specs on the battery:
Interstate Batteries Marine/RV Cranking
Group size: 24M-XHD
Cold Cranking Amps: 800
Marine Cranking Amps: 1000
Reserve Capacity: 135