I have 1000-watt inverter running from only 2 Trojan T-125 batteries. It is powering a 10 cu-ft fridge at 1-amp. I went tailgating recently without an issue. I precooled the fridge Thursday night from while plugged in to my house. I started off the trip on Friday morning, ran the generator for 4 hours. On Saturday, I ran the generator for about 4 more hours. On Sunday, I ran the generator for an hour.
Next weekend, I went on a trip 7 hours one way and then 8 hours back.
I never had a problem at any time with low batteries, but then again, I wasn't trying to go several days on the batteries alone.
I would imagine that 4 batteries would be ideal.