The Allison transmission, and most modern engines as well, are all computer controlled.. Computers eat elecricity, that's the battery's problem, when the battery goes down the computer crashes and... Well, you know what happens next.
Question: (WIth implied suggestion)
My coach has a bi-direcitonal isolator, this means if the house converter is operational the chassis is charged as well as the house. (Likewise the house is charged by the engine)
I also carry jumper cables and other means to jumper if needed.
If you have a Bi-directional isolator skip the next sentence and go the the all caps line.
Why not jumper the house and chassis batteries together and...
START THE GENERATOR to provide for battery charge?