I have thought about installing back up batteries but have put it off for the time being. The cost just now is pretty high and difficult to justify unless electricity prices stay this high in the long term. The daily gas prices, which are the main driver of electricity prices, have dropped dramatically recently and If this continues the unit price of electricity should drop.
We are due to change cars in two years time, with option of a two year extension, and i hope in this time V2G/V2H capability will be available. This will give the use of the car battery to run your home.