This depends very much on the circumstances (number of people, temperatures, consumption...). A very rough estimation: in summer you can camp for 2 to 3 days with 1 residential battery and 4 to 6 days with 2 residential batteries. But it is best to find out for yourself. It also depends on whether or not the refrigerator runs on 12V. For compression refrigerators, it is therefore always advisable to add an extra residential battery.