There are a couple of things about battery storage, a grid built on renewables needs ride through capacity and it needs to be able to meet surges in demand. In fact all grids do. Batteries do that and remove the need for hot standby gas generators but at the moment due to lack of capacity, not all fossil fuel generators. A lot of focus is on batteries as the backup for loss of wind or sun, the spread of renewables over a large geographical area and interconnected grids provides greater assurance.