There was an interesting note on RV.NET the other day during a discussion of small 120VAC compressor reefers, like dorm reefers -- One poster mentioned that small chest FREEZERS are more efficient than reefers, hold the cold air in when opened and can have the thermostat set to function at reefer temps. I can see an arrangement where a small, under-counter chest freezer is set up to tip forward for access.
It was also mentioned that in the store, the freezers/reefers have a label stating the kilowatt usage per year for comparative efficiency purposes -- This number then includes starts, stops, down time and run time over a year (presumably in the ambient temps found in a home).
To find expected battery
needs, take the annual KWh, divide by 365 (day use) , divide again by 10 (voltage conversion), and multiply by two (good battery
practice is to not use more than 50% of amp hours before recharging) -- No estimate was given for inverter efficiency.
For a small Sears dorm reefer (1.7 cu-ft, $65), the annual number is 299 KWh, so 299,000/365/10 = 82 Amp Hours @ 12VDC; multipling by two means a 160 AH battery/battery string is needed for once a day charging. The UL label indicates 120VAC; 0.8A run consumption, or 96Watts, so a 300W inverter should handle this nicely.
Of course, a custom installation with plenty of insulation on bottom and sides, plus good circulation over heat exchange grid or plate, might reduce starts and run times (this is where chest box works really well because you don't dump out the cold air when you open the door).