Batteries Dead

[Tree Top Turkeys]

2021 3761FL has two lead acid batteries. I’ve installed a negative lead knife switch disconnect so while storage I usually disconnect negative and turn the know (in error switch??) to red. The I turn and pull out red key in water panel compartment. I’ve yet to have dead batteries since owning but today after sitting less than a month both batteries were dead? I tried connecting to truck to get enough power to push open a slide and I got nothing? Any help appreciated