I do it both way here... I can pull the batteries and set on the table in the garage or I can just pull the battery cables and let them set in the battery box.
A charged up battery will not freeze up on over the winter months...
My batteries when fully charged usualy read around 12.6-7 VDC across the battery terminals... After sitting all winter long in the battery box they usually drop down to around 12.4-5VDC just sitting there disconnected...
Some folks will put a small tickle charge on them but if you do this you will want to look at your batteries every couple of weeks or so and make sure your small trickle charger is not boiling out any battery fluids over time...
I brought one of the batteries into my radio room last September to run a small power inverter if I needed for an hour or so to run a desk light. I have one of those small led monitors on it and it reads 12.5 now and flickers down to 12.4 occasionally... haven't touched it since September last year..
Roy Ken