Our local nuclear station has three enormous batteries that hold GWh of electricity for peak times. They are called Lakes Jocassee, Keowee, and Bad Creek.
During the night when the nuclear station generates excess power, water is pumped uphill through the succession of lakes. During the day, when peak demand hits, water flows downhill to generate extra power. It's efficient and relatively cheap to maintain over time.
The surfaces of Bad Creek (at the top) and Jocassee (in the middle) can fall tens of feet over the course of a few hours. Keowee (at the bottom) is maintained level as it is also the source of cooling water for the reactors.
It's a pretty cool system, and having the manmade lakes has generated billions in economic activity for the area in real estate, recreation, and tourism.