Measure battery voltage without any outside power connected. If voltage is low the converter is putting everything it has back toward the batteries and can cause this. A loose ground can too. If yoususpect bad batteries then have then evaluated to be sure.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7