Over the years I have taken out my TT batteries and hooked them to a trickle charger in my garage during each winter. I now have the TT under covered storage at a local storage yard which has electric...
I'm in Ontario where it gets cold. For the last 40 years I fully charge the 2 batteries in our boat and ensure no loads on them. For my Miata and John Deere tractor the same thing - fully charge and take off battery cables.
I leave them in Nov and come back in April. Batteries are all still mostly fully charged.
Batteries with no load on them are fine in cold weather over the whole winter