03 Sun Voyager 12V issues

[M0mmydee]

We need help please!! Our 03 Sun Voyager 8638 had flickering lights and low voltage alarm with information panel showing 9V. Slides, electric steps, fridge on gas, water heater worked then quit working when battery low. When we turn coach lights on after 2-4 minutes alarm sounds. We replaced both coach and chassis batteries, the 3 circuit breaker boxes near the batteries, (2-80A, 1-100A), the converter, cleaned all connections when installing new batteries, checked all fuses and breakers, checked battery and power connections with volt meter, all good, and still having same issues. When plugged into shore power all outlets, W/D, dishwasher, microwave, AC work. We put a trickle charger on house batteries to be able to use water heater and fridge last 2day trial trip. Any suggestions on what to check next? Thank you in advance!