This will work, obviously. But I don't see how it can be competitive with batteries. High energy density lithium batteries are currently being commoditized. Th

This will work, obviously. But I don't see how it can be competitive with batteries. High energy density lithium batteries are currently being commoditized. They are also increasingly able to handle many thousands of cycles. E.g LiFePo4 cells. The raw materials for batteries are not actually that expensive or rare, so that leaves the manufacturing. You might think that making something as complex as a battery can never be as cheap as hanging a weight from a rope. But there are examples of very complex products (solar cells, LCD displays) that became incredibly cheap due to mass manufacturing. A square meter of solar cells, requiring extremely pure silicon and nanometer scale engineering, is now not much more expensive than a square meter of good roofing shingles.