You probably have bad batteries if they haven't been charged in awhile. The deep cycle batteries should never be allowed to drop below the 12.0VDC level.
You probably have boiled out the fluids and the battery has gone bad on you now...
Using a meter across the battery terminals should read 12.6-7VDC when fully charged and if it reads below 10VDC then it is basically a dead battery... My shorted out batteries usually only read 5VDC when measured.
The PD9100 and 9200 series smart mode chargers will take care of your batteries for you when you finally get a good battery to maintain...
There may be problems with your wiring or switching as well for the system not working and this is why you need to measure across the battery terminals to see what the DC Voltage level reads there...
I always look at the battery to read where the NEGATIVE TERMINAL is located...(Says NEG or SYMBOL '-').. Then I make sure this battery cable goes directly to frame ground close to the battery... If this has ever been wired wrong then you will have some blown fuses in the the path to the converter/charger unit.
Connecting the multimeter to the battery terminals is also good for making sure it is getting a charge voltage. Like said above it should read 12.6-7VDC with no shore power on and is fully charged. If you connect to shore power and the converter/charger comes on line then this DC Voltage should jump up to 13.6VDC or higher depending what charge mode it is going into. Mine will read as high as 14.4VDC when in boost charge mode. If you don't see this increase of DC voltage then something is not connected from the battery terminals to the DC output terminals of the converter/charger unit. Or perhaps the converter/charger unit is not turned on from the 120VAC side...
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
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