That was the setup at our previous home. We had a two day power outage in the heat of summer and it kept the fridge running. The car had to started a few times to keep the battery up. One of the key to keeping items in the fridge cool is not open unless absolutely necessary and then only long enough to retrieve what you need. Another hint for the freezer is to add ballast (Ballast, is that the right word? Thermal mass?). If your freezer is not packed with food fill the empty spots with large blue-ice.
A more elegant solution might be a gas generator.
