This switch can be used to provide emergency starting power from the house batteries if the chassis batteries are dead.
Press and hold while turning ignition key for emergency starting power.
This switch will add the house batteries to your chassis batteries for additional power.
The best procedure, as described by Coach-Net, is to:
1. start the generator and run for a couple of minutes to put juice into your house batteries.
2. Then, with the generator still running, hold down the Battery Boost switch for 45 seconds or longer to put some juice into the chassis batteries.
3. With the generator still running and the switch still depressed, turn the ignition key.
While the engine is running the house Batteries AND the Chassis batteries are charged.