so-called “gravity batteries” is pretty much exactly a dam with a mini-dam/reservoir at the bottom. When there is an excess, you run the motor to reverse the waterflow to pump uphill into a highe-elevation water retention pond/mini-dam.
This also helps reduce the amount of outflow water “lost” due to high-demand. Since you could take almost a day to fill the bottom reservoir and spend “wind”/solar to pump back the “lost” water downstream back into the higher-level reservoir.
Even if things are inefficient wind/solar are “renewable”, so you can keep “wasting” excess to replenish the dam and still make enough money back ( think in-terms of drought, flooding, windy, sunny, cloudy, etc ) you can basically keep the high-output “system” always topped-up with water. And still supply water + electricity as it is needed. There is no “downside”.
Not everyone agrees. So opinions can differ.
Get shots, pay health insurance. Dont get shots, life insurance pays your loved ones.
Macabre and sadly true.