We have a 2014 377xl. Parked at outer banks NC in the summer on our 8 week trip. Was there for a week and played the radio everyday and used the dash switch. When we got ready to leave the engine battery was dead. The transfer boost switch could not provide enough voltage to jump the engine. Got a jump and went on our way. Had batteries tested and the house batteries where all bad (3) engine battery was of same make but was ok just low. By the way the coach had just 1000 miles on it and yes I'm a maint freak and the batteries where watered prior to leaving. Long story short, ran the engine every day for 15 mins to charge the engine battery and the coach was fine on house current (50a). When we got back to the dealer we had all batteries replaced new and found that no matter what when the engine battery was disconnected the radio would not play regardless of the dash switch position or house current etc. The radio for some strange reason runs off the engine battery the dash switch just bypasses the ignition switch/key. Had the dealer switch the radio feed to the house batteries and all is good except that when you hit your disconnect switch you lose radio time and station memory. Not a big deal to us because we are always moving and Sirius radio hold the memory in their program.
I have confirmed the wiring to the engine battery both by dealer tech AND FR factory. Sad design but as they say we own it now.