It's technically possible to replace rotating mass with batteries using a "grid-forming inverter", which is an inverter that converts the battery DC to AC with frequency varying depending on the grid load, simulating how that rotating mass would behave ("synthetic inertia"):

https://en.wikipedia.org/wiki/Inverter-based_resource#Grid-f...

This competes with the traditional giant flywheel option ( https://en.wikipedia.org/wiki/Synchronous_condenser ), which has the advantage of being a simple and proven technology, and handling brief overload better, but the disadvantage of having moving parts. It's not clear which option is currently best. Both are in current use.