Another "battery" would be an electric train - say 100 electric locomotives all coupled together.
Now all one needs to do is find a conical mountain and build a spiral track around and around all the way to the top.
When the wind is blowing and the sun is shining this "battery train" uses the grid to power its electric motors and go from ground zero to a nice high level full of potential energy.
When the wind stops blowing and the sun don't shine no more, then it's toot toot, and the battery train using gravity (like hydro), trundles it's way to the bottom (like it's on a helter-skelter), with all the electric motors becoming generators and back feeding the grid.
