Underprovision? Pour some more concrete, truck a couple more batteries in.
Overprovision? Load em up again and resell them to someone who wants them. Can't quite do that with a gas plant.
Sure there will be some overhead lost, but it just make soooo much sense to go with battiers from a risk perspective.
They also look (but I'm a layman) easily maintainable, more like server racks than high tension electricity stations. I wonder if the batteries would be hot swappable.