The batteries should be maintained all winter long....depending on the condition of the batteries it is possible that they could freeze and split causing a huge problem come spring......I just leave my on-board charger plugged in all winter long (it's actually plugged in ANY TIME I'm not fishing) and this maintains the batteries for a MUCH longer battery life.
If you don't have a on-board charging system, then I would pull the batteries and place them in the garage or basement on a piece of wood (old school)....charge them once a month....set a alarm in you cell phone for once a month or use Gmail calendars that email you.
Now how's that snow blower running....it's that time of the year....