Isn't gravity based the thing where the mechanism is, crudely, a rock tied to a rope gets lifted, then the mechanism locks it, and when energy is needed the lock releases, dropping the rock and spinning the turbine?
Takes more energy to lift the rock, but the lock costs almost no energy, and when energy depletes, the lock releases, drops the rock, and offers reserve energy.
Basically all electricity generation, but a rock and a rope.