Batteries are definitely off the boat. Even for a single winter, I never leave them on board... They are on a marine charger in the basement at my in-laws. They were at the end of their useful life anyway so I will probably replace them.
I went to great pains to remove anything that could freeze, or cause damage or be damaged by the humidity (summer) or cold (winter).
Now based in Barbados.... and wait for it.....the boat is too!
Waymar - Jeanneau, Attalia