how does a battery boost switch operate?

The switch on the dash energizes a relay to connect the two battery systems together, chassis and coach. On some the relay is also the charge relay that allows the chassis alternator to charge the coach batteries.

If it is working right, it operates a big solenoid switch that ties the two battery banks together (engine battery and house batteries).

It is fairly common for the solenoids to go bad.....as they can carry a LOT of current when used.

Also on Winnebagos the RUN terminal on the ignition switch activates the boost solenoid so the house batteries are charged while driving. The boost solenoid is a continuous duty solenoid.

A little light reading - Intellitec Battery Control Center

This is just one example of multiple configurations. Specifically this version includes the disconnect switches, AUX Start and changing of both the chassis and house batteries from either the alternator or the converter/charger.

All good answers!

All of the above are possible configurations of how it might be wired
All configurations use at last one relay
Some systems use more relays
Make model and year of RV , will help us be more specific
Someone may have the same RV

Clay L wrote:
Also on Winnebagos the RUN terminal on the ignition switch activates the boost solenoid so the house batteries are charged while driving. The boost solenoid is a continuous duty solenoid.

Do they still do that?

While all the above answers are correct, to give a quick answer to what the OP may have been asking,
When pressed it basically acts like connecting jumper cables from one battery (or batteries) to the other.

Not all systems that connect the chassis and house batteries have a relay involved. Some operate a regular battery solenoid that connects the two battery systems.

garym114 wrote:
Not all systems that connect the chassis and house batteries have a relay involved. Some operate a regular battery solenoid that connects the two battery systems.

People are using Relay and Solenoid as the same item. Battery Boost---It takes a COACH battery system fully charged to activate the Battery Boost. If your Coach batteries are dead or below 11.5 volts the system will NOT activate. And if it does close the solenoid nothing will happen because the Coach batteries are below 12 volts. Remember, IF the CHASSIS batteries are fully dead, the Battery boost may not work on a Diesel Motorhome. THE AMP DRAW for a Diesel battery system is to great for some boost solenoids to transfer enough amps to start the engine. The dead chassis battery will "draw" some of the current that is needed to the starter. GAS engines will usually start with a dead Chassis battery and using the Boost. Doug