House Batteries Dead

On most coaches, the "Battery Boost" switch operates a solenoid. The power for that solenoid comes from the house batteries, because it is assumed that the starting battery is dead, hence the need for the "Battery Boost". If the house batteries are dead, you cannot use the switch to energize the solenoid. Might work if the house batteries are just too weak to crank over the generator but have enough juice left to energize the solenoid. Best to just start the engine and let the alternator put some charge back into the house batteries.

FYI, it takes hours of generator run time to put a decent charge level back into the house batteries.