I just bought a Trail Lite B+ 211s with 8.1 Chevy engine. This is my fifth motorhome (others range from an old 20' Vagabond, and three Winnegagos, from 19 to 32'. This vehicle is fantastic. I am...
When the engine is running, the batteries are connected. When you press and hold the EM Start switch, IF the house battery is online ("Use" mode), the batteries are connected. All other times the batteries are separated.
If yours is not functioning that way then something is wrong or at least set up differently. I can offer suggestions to see if the engine isolator solenoid is working properly.