Assume a 3000 ft hole in the ground. A block of lead 10 ft x 10ft by 12 feet high. That's 422 tons. That's would store 955 kW-hrs of energy. If the block drops into the hole by cable in The power is 955 kW. I looked up the working load for steel cable 2" in diameter. 13 cables would do it. But of course you would want an even number. The cable weight is 133 tons. That's 32% of the pay load. But that will contribute to stored energy. Also means you need more cable.
It's not impossible.
Sure it's not impossible, mearly impactical.
Cranes need maintainence, lots of it. Cables wear and break, pulleys wear and break, bearings, motors, shafts, gears and couplings all wear and break, even brakes, er break.
Look at a typical pumped hydro scheme for reference. Even here with a very robust system with just a couple of moving parts (motor/generator, pump and valve block) and using a working fluid that is effectively free, these schemes "generate" electricity (they are of course net consumers of electricity....) that is very very expensive, and even with a huge lake of millions of tonnes of water, 1,000's of feet up a mountain the energy they can store is actually quite limited......