You gave us no useful information at all!
Do you have a motor-home, or towing some type of trailer?
How old is the RV, and battery(s)?
Does the battery have a disconnect switch? If not turned "on" the battery could not be charged, but most converter/chargers would supply 12 volt power while plugged in.
It does not sound like you bothered to use a multi-meter to check actual voltage at the battery-terminal (while RV was unplugged) to see what it's voltage was to begin with (should have been 12.6+ volts).
It could be an old or bad battery, loose ground, disconnect switch, or converter/charger, depending on further testing.
By the way; if the battery is below 11 volts a good converter/charger may not start charging the battery. You will need to use a portable charger set to around 2 amps to bring the battery voltage up to around 11.5 + volts before the converter/charger would start to work.
If you have only a 7-pin connector charging would only amount to around 10 amps charging for each hour driving. Not nearly enough time to charge a dead battery.