[gnramires]

Those methods are actually quite similar, they're all ultimately related (limited by) tensile strength of materials. So costs and specific energy densities (per construction material unit) are similar. An important figure is cost/tensile strenght I guess.

(Compressed air: limited by container tensile strength; gravity batteries: limited by strength of cables)

I suspect even the constants involved are the same (given the materials are almost uniformly under nominal load), although I don't have time to investigate right now (a good curiosity research topic!).

[istjohn]

They are storing liquid air at low pressure, so container tensile strength is not a limiting factor at all.

[trickstra]

I believe these ones are not limited by tensile strength: https://interestingengineering.com/concrete-gravity-trains-m.... They are a bit limited by available geography, but far less than say pumped hydro.

[gnramires]

Indeed! In this case it's the integrity and friction of the soil (of the hill) that's keeping the potential energy contained, and this hill soil is "free".