12 volt refridgerator

Look on your batteries and see what their reserve is. Then do the math, divide the reserve by the load. For example a 100 amp/hour battery would thoeretically run your fridge for 40 hours. If you had two 100 amp/hour batteries you could run 80 hours. Not exact but that's the idea behind those ratings. Your fridge is theoretically using 30 watts of power, VxA, or 12x2.5=30.