Yes, it is fairly common to have coach and eng. batteries drained if you don't have disconnect switches on the batteries. Seems there is always a parasitic drain on coaches elec. and difficult to track down. Most folks just add knife switches on their batteries.
Your battery may be toast now if it has been drained all the way down for a long period of time. You may want to get the battery tested.
2015 Thor Vegas 24.1 in Ocala