Suppose you have standard rail tracks and use a surplus freight train. Congratulations, you can now store the amount of energy needed to push a single train up

Suppose you have standard rail tracks and use a surplus freight train. Congratulations, you can now store the amount of energy needed to push a single train up a single mountain. That's not nothing, but it probably isn't enough to be useful on a utility scale. That implies that you want a weight orders of magnitude more than a train (or many trains per charge "cycle" with a stockyard at each and of the mountain to store them) You're now going to need a very tough track and wheelset. They're also going to wear quickly. Probably enough to make it impractical to build and operate.