Not sure if you store the camper where it cannot be plugged in. If so and the battery was not disconnected the camper has some "parasitic" draw and will drain the battery. If it drained completely down then the battery may be bad and not take a charge.
This may sound strange but a cousin bought a new camper and always went to campgrounds with hook-ups. We all went to a campground with no hook-ups and they also had no lights. After checking fuses we checked the battery and the dealer had not installed one.