I have two 100 amp hour batteries in my Kodiak Cub. They last a couple of weeks without the disconnect. They last several months with the disconnect turned off.
I always start with a full 18 hour shore power charge. Then I shut them off. The battery manufacturer says my AGM batteries will hold a full charge for 12 months if they are disconnected.
You can get battery disconnect switches and most automotive stores and departments. Or, you can just remove the negative cable from the battery.
I wish you good luck and happy trails ahead!