If you overprovision the electricity production you can get away with less battery capacity. It’s a tradeoff and the cost-optimal point is not going to be the one where the production is exactly equal to the demand.
Yes that's why no one is going for 100% currently yearly production match with renewable, it will need to go higher in production :).
Then you'll get times with overproduction with very low prices, this will prop up "power to storage for power later" (liquid, gaz, whatever) with buy low sell high usual market stuff.
Note that France has currently 130 TWh of gaz storage capacity for about 473 TWh of yearly electricity consumption.