12V/120V freezers do exist and are marketed towards RV, camping, and off grid markets. Disadvantage is they tend to be smaller, cost more. But they are very efficient. Where a residential freezer might draw a couple of hundred watts dual voltage fridges draw 25-50 watts. And automatically switch between 12VDC and 120VAC. So they can be connected to both shore power and a battery at the same time and it 'just works'
There are also propane fridges/freezers but they are also smaller. (Though at the point where you have a large propane tank, you could arguably just as well have a backup generator.)
My impression is the big advantage of absorption fridges is they will run off a tank of propane for a long time. But Downside they are very slow to cool down and running off AC/DC they aren't very efficient.
But yeah cheapest thing to do is get a furnace transfer switch and a generator. That seems to be how rural people in the upper midwest avoid freezing to death when the power goes out in the winter.
