It is hard to say remotely. However if your batteries are truly dead to the point of being unchargeable, the converter may see them as a short circuit and not provide any power. I would suggest disconnecting the ground cable from the batteries, and see if the converter alone will provide any power.
If you want to attempt to resurrect the batteries, try to charge them with a external charger while they are disconnected from the coach.
Personally I'd say they are toast.