Generally LFP with cycles in the at least 5000 range.

They are pure arbiters of the market. Filling up when it makes sense and delivering when it makes sense. Which sometimes means buying expensive fossil gas powered electricity to sell it even higher priced later.

But what this means is that at that ”later” the peaking plant that originally has been used did not have to start and consumers enjoy cheaper electricity.

But what they do is extend the time renewables deliver. In for example California storage has reduced fossil gas usage by 40% in recent years.