I hookup a aimes 2500 inverter to two 6 volt batteries. Seems all was good and working fine. When I was hook up to shore power the inverter would switch and start charging. Today I was hook up to a 11...
+1 inverter was trying to power a/c. I don't know what model or inverter you have, but the generic 2500 inverter doesn't list pass through power as an option meaning it doesn't have an internal transfer switch to turn off the inverter part of the box when 120V is available. Being rated at 20 amps output, the inverter may be capable to run the a/c. But as you've learned, the battery cables seem undersized.