A "peaker" or Open Cycle Gas Turbine is much less efficient which is doubly expensive in Europe. Firstly you need more fuel, and the fuel is expensive, but also you're making more pollution and that's expensive too.

The UK for example basically doesn't have "peakers". Right now it's early evening, demand is high as people cook evening meals but haven't yet retired to bed where they stop using electricity, but renewable generation is reduced as the sun approaches the horizon. So there's 8GW of combined cycle gas power plant production, but only about 100MW of "peakers" and it might grow to 200MW or so at absolute peak.

This is the exact scenario they are being used in at scale. The company removes their gas peaker plant infrastructure and replaces them with batteries. Already have the grid interconnect and now can dispatch power on the millisecond level instead of hour level.