The battery power is used to run the control boards. It should take very little power from your battery (depending upon the quality of your battery). If your RV is parked at home, simply run the fridge on propane for 24 hours and then see how much power the fridge takes from the battery. Each fridge/RV/battery is different as to usage, so it's better to know yourself.
With my 1975 Dometic fridge and a Group 31 AGM deep cycle battery, I don't put a dent into my battery power over 4 days (including use of the water pump and lights without being miserly).