The 500wh/kg figures come from at least two companies nine months ago - one might be a US arm of the other:
https://www.catl.com/en/news/6015.html
https://amprius.com/the-all-new-amprius-500-wh-kg-battery-pl...
Both have asserted idependant verification.
High energy density isn't the only desirable goal of course. Really cheap, bulk storage, hard to damage, with long lifetime and many recharge cycle batteries are good for grids even if they're too heavy for the mobile | car market.
https://en.wikipedia.org/wiki/Vanadium_redox_battery
,for example, have a promising future in not { car | phone } applications.