Before I condemned my batteries, I would have the charging system checked.
A low voltage indication, while driving, points to a fault in the charging system.
Once you stop, the batteries, that were carring the electric load, would fail a battery test.
If you can start the MH ( Try the Boost Switch ) you can check the battery voltage, while running. Look for more then 13.5 volts.
If it's a charging system, you may be able to continue your travels with the generator running and the boost switch held on.