For fun, let's say you have a 20-ton container, and you raise it up the rail by 100m. The stored gravitational energy is about 5.5 kWh.

According to Wikipedia, Tesla Powerwall 3 has 13.5 kWh of capacity: more than two 20-ton containers raised to 100m, assuming perfect efficiency. It costs $7,300, small enough to put in your house, and also (more or less) safe enough to put in your house, unlike a 20-ton container on a rail barreling down a slope, which probably needs professional hard-hat maintenance crew.

So consider me skeptical.