There are a lot of variables.
The EPA energy guide numbers might be a reasonable starting point. Typical for fridges these days are around a kWh per day, maybe a little less for comparatively small fridges, particularly those without ice makers and in-door water dispensers. Very little dorm fridges often use pretty nearly as much energy as smallish full-sized fridges.
Your battery bank is about 450 Ah at 12V, or 5.4 kWh, and about half that is all that ought to be used for the batteries to last well. Two days of use would not be unreasonable as a very rough guess assuming there's nothing much else consuming power at the same time. Obviously it's far more accurate to measure your actual usage and work from there.
