that requires specialized equipment other than the battery. you need to generate AC from the DC of the panels and battery, and the easiest way to do that at the right frequency and phase is to follow the grid. that's why most solar installations stop providing power without a grid connection; you need a wave to sync with.

if you want to be truly independent you need your own wave forming equipment. and not the cheap stuff either, like the 12V inverters for cars that give out square waves. that's fine for like a drill, but plug a computer into that and there's a chance it fries. it won't charge, at least not for long.

also you need extra safeguards to not fry electrical workers when they disable the grid and your power comes flowing the other way.