When I tried to close the slides without shore power, my fridge panel showed 'Low D C'. Checked the battery. It was not charging. Found a tripped breaker in my converter. Flipped it on and battery was charging again at 13.31 Volts. Figured all was good. Next time I closed the slides off shore power same thing happened. No open breaker this time. Started truck with umbilical plugged in. Battery again showed 13.3 volts charging. After fully charging again the battery went flat at 10.7 Volts.
I replaced the battery. All is good again.
I think you have a similar problem. Buy a battery.