Batteries do not replace power generation capacity directly. They can, however, be configured to cover huge surge loads for short moments, or smooth out small

Batteries do not replace power generation capacity directly. They can, however, be configured to cover huge surge loads for short moments, or smooth out small discrepancies over a longer span, in more or less the same footprint. If you want a GW of coal, you need a GW plant, whereas with batteries you can decide between a gigawatt-hour or a 1000 megawatt-hour using a similiar footprint (scale to capacity of chosen technology). This reduces the need for significant unclean backup capacity, and either decommissioning them or reducing their usage.