Are the two new batteries 12VDC batteries or 6VDC batteries...
If they are 6VDC batteries they must be connected in series to give you 12VDC to supply your system with...
About the only thing that will blow the 30A FUSES that are off to them self (The GREEN Ones) is cables going to the batteries connected wrong, batteries are not connected together correctly, or a dead cell in the battery drawing alot of DC current.
If your two batteries are 12VDC they are to be connected in Parallel. If they are 6VDC batteries then they must be connected in series...
Other note is the older parallax converter/charger is not one of the smart mode chargers and should be replaced for a smart mode version converter/charger. The smart mode converter/chargers will almost take care of your batteries automatically...
Roy Ken
