When did lead-acid stop being cheaper than any version of lithium?
Of course, on a Total Cost of Ownership (TCO) basis, it was already cheaper quite a while ago (for the last 5 years I'd guess). It was a combination of LiFePO4 batteries having such longer cycle lives than any lead-acid chemistry, and the greater depth of discharge meaning you could use a lot more of the energy. So if you build a new lead-acid based system, you'd need almost double the amp-hours of batteries to supply the same amount of energy with a safe depth of discharge, and you'd still have to replace them much sooner. So you'd not only have to factor buying a lot more batteries with lead acid but also replacing all the lead acid batteries at least once while a LiFePO4 system would continue to operate.
So if you think about the amount of materials - lead acid are almost double the weight vs. lithium batteries per amp hour to start with, then multiply by two because of the usable capacity difference, times four to eight for the cycle life… So you’re talking having to recycle something like sixteen to thirty-two times the weight of the lithium batteries in lead, before the LiFePO4 batteries would have even reached their end of life!
It’s really almost unbelievable how much better and cheaper the lithium batteries have become!