It is a bit of how long is a piece of string I'm afraid. I only have a 70ah (albeit AGM which I am led to believe is as good as a 100ah wet battery) and, with my fridge running, occasional water pump and a few hours of lights (LED) we only get around 2 days off grid (lights and water pump will run longer but fridge compressor wont run once the battery drops below a certain voltage). I now have a 100w solar panel and I think in the summer I could run pretty much indefinitely off grid.