When was the last time YOU checked those house battery water levels?
Batteries boiled dry......
Converter (charging section) over charged batteries.....boiled the water/acid out and they are RUINED...DEAD......SHORTED.
You need new house batteries
You need to check the DC output of your converter (13.2 min/14.4 max) and that converter actually comes out of bulk charge mode (14.4)
Battery disconnect switch did not cause batteries to be overcharged and water to boil out.
Hard to install it wrong....it only gets installed on one cable -----positive normally but can be on negative.
Neither would cause your issue
Turning on inverter would have just placed a load on batteries....which were already damaged.
Edited for spelling :S