What failed in the technology?

Because batteries are the only part you can criticize, take a look at the sodium batteries made by CATL:

https://cnevpost.com/2025/12/29/catl-expects-sodium-batterie...

https://carnewschina.com/2025/12/28/catl-confirms-2026-large...

It's a real breakthrough in battery tech. With gasoline you simply can't have this.