If you have a rv fridge, Dometic or Norcold, it should run off 110 volt shore power or propane & if set to "auto" will switch between the 2 as needed, both of which require 12 volts from batteries to power the control board.
If you have a residential fridge it runs off your battery bank through an inverter, for it to run very long will require more than 1 battery.
As stated, more information on your rv would be of great help to those of us trying to help, add to your signature.
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