RC is reserve capacity. A fully charged battery will last for 390 minutes or 6.5 hours without being recharged with a 25 amp load before being brought down to 10.5 volts (for a 12 volt battery). This is lower than you would want to discharge your battery on a regular basis but you could in an emergency.
A 21 cubic foot residential side by side refrigerator uses about 780 watts of electricity at 120 volts (6.5 amps). Assuming a 94% efficiency factor for your inverter, at 12 volts that would suck up 1660 AHr a day if it ran 100% of the time. However, typically, a refrigerator runs about 33% of the time or about 553 AHr per 24 hour period. At higher loads, batteries don't hold up as long as they do at lower loads (as shown in Interstates chart of 38 hrs at 5 amps (190 AHr) vs 6.5 hrs at 25 amps (162.5 AHr). When the compressor is running you are pulling about 70 amps. Spread across two batteries that is still 35 amps/battery. That is one of the reasons that more batteries are good. If you could feed the refrigerator off of 3 batteries you would be pulling 23 amps/battery and the 162 AHr would apply. Since they don't show the hours of life at 35 amps we can only guess that it is likely less than 140 AHr or about 4 hours. With the refrigerator cycling (assuming the refrigerator is already cold and isn't having to run 100% of the time to cool itself down), two batteries should give you about 280 AHr or about 12 hours BUT that takes the batteries down to 10.5 volts and you REALLY don't want to do that. Realistically, the two batteries would likely need a recharge about every 6 hours. That is the reason that Newell's switch to residential refrigerators was matched with an increase in the number of house batteries from 2-8D's to 6-8D's and a 400 amp alternator.
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