I guess sipping electricity is relative. That 3.5 amps @ 120 is 35 amps @ 12 volts. That means the refrigerator will take an averaged sized RV battery down to 50% in about 90 minutes of continuous run time.
I have timed my NovaKool which pulls less than 1/10th the amps. It might run at about 30% if everything inside is cold, and the door is not opened, and the ambient temp is about 70 degrees. If the ambient climbs to 80 then it seems to run more like 70%. Add a few more degrees, which is plenty common in the Summer and my unit will run pretty much continuously.