Start Battery Discharge

[Colvin Cottage]

I recently acquired a class a RV and I'm battling the engine battery discharging while having the switch flipped to AUX batteries so I can run the stereo with the ignition off, when having the generator or plugged into shore power the shore batteries will charge but the engine battery will discharge which is odd because the systems should be separate since the engine battery doesn't charge while the switch is on AUX but it still discharges.

Other that mounting an external maintainer and running a power line to a maintainer to charge the start battery while plugged into shore I'm kind of lost.

I did find a thread about replacing the AUX switch with a double pol switch but was a little unclear if it worked

[DavisK]

You could install a battery isolator on the main battery. It will allow the engine's alternator to charge both batteries when the engine is running. It would also allow the coach to drain from the auxiliary battery but not the main battery when the engine is not running. That is how General Motors set up the battery systems in their diesel pickups.