I think some of it's subjective and depends on the lighting set up and needs for the scene. If you need those huge lights that will light up a city block then you will need a generator.
It is all good until your battery runs out and you still have a lot of projects to film. Also as Kim said, it could work only if you don't need powerful equipment
What kind of battery could power a huge light? I mean it could work for little lights but when the work get serious I highly doubt they are even an option.....