I was curious about the possibility of essentially using hydraulics, a gearbox, and spring for energy storage. For example what is the feasibility of using a large coil spring with a compression distance of say 5 ft, with a pressure of something like 50,000 PSI. This is the battery cell, to recharge it is a hydraulic cylinder and pump wouldn't take any more than a few minutes I think to reset the spring, with a gear reduction clockwork mechanism for power output. Could the stored energy of the spring be used to compress a second spring by way of hydraulics?