[marktwain]

400watt hours is about half the performance of lithium.

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Maybe in items not used widely now.
According to this article, Lithium-ion batteries are in the 160-250 Wh/kg.

https://www.laserax.com/blog/solid-state-vs-lithium-ion-batteries

[Jonty30]

I had read that they got it up to about 800 wh/kg.

My mistake.