Here is a start. When you finish that do another search and use the word BIRD for subject or content.
Are you plugged into shoreline?
Do you have a solar panel?
If you have a solar panel and now clean terminals the solar may be causing a "BIRD" to activate the aux start/combining solenoid. With one bank of batteries low the voltage is pulled low enough to cause the "BIRD" to shut off.
Plug in to shoreline and charge things up, then see if the problem goes away.