You should have an inverter charger built into the RV that charges the battery when plugged into shore power. It is good practice to disconnect your battery when storing the RV, as lots of things have parasitic drain on the battery. Draining a new battery down to zero will kill it dead. If you are saying a known good battery isn’t being charged by your inverter when plugged into shore power then you either have a bad inverter or a bad connection.
