Great idea. Why didn't we think of this sooner?

However, besides the EROEI problem in operation (lifting the weigh and having it descent slowly rather than crashing which will consume more energy), consider that the global production of iron ore is 2.4 billion tons i.e 2400 billion kg, good for less than 6700 batteries 100mwh each, .67 terawatts if we exclusively use it for batteries not not steel for other needs etc.

The global electricity consumption (2019) was 23,900 terawatts per statista.com let’s round to 24,000

That’s 24,000,000,000 Mwh

Someone check my math but that sounds like 35,800 years of iron production just for the weight.

Better start digging.

(BTW The total energy required to extract and process iron is 94,400 Btu per ton which of course we get from fossil fuels)