Chassis Battery's are losing charge while driving

[Wheelwright]

While driving in the winter with my Aqua Hot on, my chassis batteries are losing their charge.  My alternator is showing 13.9 volts.  The house batteries are staying up, but the chassis battery discharge.  When I stop the coach and try to restart, the chassis batteries are too low to engage the starter and the Battery Boost switch will not work.  I have to run the generator for about two hours to charge the chassis batteries enough to start.  House and Chassis batteries charge up and test out good at home.  A test of the Alternator voltage confirms the gauge 13.9 volts.  If I just turn on the key, I can get the Battery Boost switch to work.  Should the Big Boy Relay energize and stay energized with the engine running? Both House and Chassis batteries are showing 13 plus volts.

[Bootlegger]

Sounds like a bad cell in one of your batteries.  I went through 3 batteries in as many months on my wife's SUV.  The dealership blamed bad batteries made during covid.  

[Frank Bergamo]

JC,

Check the voltage on the big terminals on both sides of the Big Boy solenoid. They should be very close if big boy is operating properly. The Big Boy corrodes inside on the contacts, preventing proper charging of battery banks. If voltage is not the same, then removing Big Boy to clean contacts is not that big of a job. Hope this helps.

[Jdw12345]

Maybe this will help.

Big Boy Relay rebuild instructions.pdf

Edited March 10, 2022 by Jdw12345