Looking online I saw that refrigerators don't usually draw a lot of wattage, they just have a spike each time they start up. Everything I found said a 1500W power inverter should be more than enough, and I already had one of those, so I decided to try it. Some people had gotten by with a 1000W inverter.
It is just the inverter hooked to a deep cycle battery, and the fridge plugs into the inverter.
How long it lasts would depend on how much power the fridge uses and the size of the battery, and I guess also the efficiency of the inverter.
The inverter is kind of like this one. I can get the exact model later if that is important.
https://www.cobra.com/collections/p...MIxLLPkYaC3gIVk4rICh2iGwH4EAQYAyABEgLAE_D_BwE
In fact, it may be that exact power inverter, just rebranded. The outlets and the power display look the same as what I have.
For the battery, get the biggest one you are OK to carry over to your refrigerator and have sitting there beside it while the power is out.
and of course the battery needs to be charged before the power outage.
If it was an extended power outage, you would need to have multiple batteries to cover a longer time period, or if you have a generator running during the day, you could power the fridge from the generator each day and also run a battery charger to recharge your battery each day so it would be ready for the night