Two stories I found, that both provide insight

https://cleantechnica.com/2020/06/10/usas-battery500-initiat...

https://www.nasa.gov/sites/default/files/atoms/files/650_whk...

There is a company called Sion Power that claims to have 500 Wh/kg batteries [0]. "With supply dates beginning in mid-2021 for UAV markets. Broader distribution for the Licerion-HE is scheduled for early 2022."

[0]: https://sionpower.com/2020/sion-power-demonstrates-key-elect...

We're there:

https://www.amprius.com/technology/

Just not at scale and naturally such batteries are expensive.

I believe lithium iron phosphate tends to be around 120-150 Wh/kg, pretty decent regular lithium ion tends to be around 150, fairly recent Tesla battery packs are a bit over 200.

(These are types of batteries that have been around for years that you can easily buy as a normal person for a reasonable cost. There's probably a lot of fancy/new battery technology that is somewhat better but either not mass-produced yet or otherwise prohibitively expensive, or trades off some other desirable quality like safety or durability to get more capacity.)

Commercially and at a reasonable cost? Probably at least 8-10 years from now.

I think Musk recently said they are going to have 400 Wh/kg in 3-4 years. So maybe 2030.