Hi Drag Racer,
The batteries normally will be charged by the converter anytime you are powered from the generator or plugged into campground power. That is assuming that the converter is operating correctly, and that no 12-volt circuit breaker between the batteries and the converter is tripped.
The batteries should also be charging when the vehicle motor is running, from the alternator circuit.
Now, batteries at the 8 volt level are REALLY DEAD, so it's possible that they just won't hold a charge at all. If these batteries are the typical lead acid type, it's important to check and fill the cells with distilled water or the lead plates will soon be toast. It's likely too late to save your batteries now.
Get a voltmeter on the batteries while plugged in to be sure the voltage is above 13 volts or more, to prove the charging circuit (converter) is working.
__________________
|