The chassis battery starts the engine and runs the dash. On most motorhomes it is separate from the house batteries, and kept separate on purpose, so running the lights all night can't leave you unable to start.
Where it lives
- Class C motorhomes built on Ford, Chevrolet or Mercedes-Benz Sprinter chassis usually have the starting battery under the hood, like a van or truck. Some have a second one.
- Gas Class A motorhomes often have the chassis battery in a compartment near the front, or a pull-out tray. Location varies by builder.
- Diesel pushers usually use two or more large starting batteries, often in a rear or side compartment near the engine.
- Class B vans have the starting battery under the hood or under the floor, depending on the chassis.
See our guide to Class A, B and C motorhome batteries for more.
Why chassis batteries die
Motorhomes sit. A lot. A chassis battery that sits for weeks with small loads on it (radio memory, engine computer, CO detector on some setups) drains, and a lead-acid battery that sits discharged in Florida heat gets damaged quickly. That is why so many of our calls are "it was fine when we parked it."
The boost switch
Many motorhomes have an emergency start or "aux start" button on the dash that ties the house batteries to the chassis battery for a jump. If the house bank is charged, that can get you started. If you have used it and still can't start, call us. Read what to do when a dead RV battery leaves you stuck.
What we do
Test the battery and the alternator output, check the cables and the battery isolator or boost solenoid, and replace the battery if it has failed. Diesel pushers get matched batteries so they share the load. Then we start it, and confirm it charges.
Questions we get about this
Can I just jump it?
If the battery is good but drained, yes. If it is failing, a jump just gets you to the next stop. We test to tell the difference. RV jump start.
Should both diesel starting batteries be replaced together?
Generally yes. They are wired together, and a new one paired with an old one works harder and wears faster.
Why won't my house batteries charge my chassis battery?
Many motorhomes charge the house batteries from the alternator but only charge the chassis battery when driving. Some have a small charger or "trickle" circuit for it. If yours doesn't, a storage plan matters.