Wind up power such as the ribbon springs used in clocks for instance. Instead of concentrating on one spring that basically turns one shaft, stack several springs together wound up tight on one shaft and release the springs consecutively. As soon and one spring winds down, the next spring's energy is released and so on down the line. Winding the springs back up could be done the same way or not. Wind them all at the same time with the single shaft. Let's use some worm drive gear combination. Worm drive has a lot of power and can be safer because if you let go the worm drive won't release and go backwards.
I picture a ribbon spring in a cylindrical, disk shaped container stacked on or next to another like records in a jute box. With a standard size(manageable size) it can be used as a mechanical battery. Double the power by releasing 2 at the same time. Windup revisited.
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