If I am plugged into shore power, the truck is unplugged. When on shore power the process is reversed and the RV charger is supplying 12v back through the umbilical cord. IMO the 12v that is being supplied is not that clean or regulated and I don't like the idea of feeding it to the TV with all the computers these days.
If I am not on shore power and overnighting in a truck stop...the umbilical stays plugged in. If I wake up to a dead battery, no big deal as I am always a member of a Roadside Assistance company. It hasn't happened yet though as I have dual batteries in the 5er and the TV.