I park 3 cars for the winter and head south for the winter.
I disconnect the negative post of the battery and let the batteries freeze for the winter, fully charged of course. For the past 7 years I just reconnect the negative post in the spring when I return, then I start one car after the other and they never fail to start on their own power. One battery is now 8 years old and still a great performer.
When I use to park the RV for the winter I did the same thing and Batteries lasted up to 6 year. Since fulltiming and never parking the trailer over winter, the batteries have been failling much more often.