China's regulators have recently issued an official definition of "solid state battery".[1] This applies to advertising, and, importantly, to investment fund-raising. Semi solid state batteries, with gels or some liquid, do not qualify. They will officially be called “hybrid solid-liquid battery.”

The test is simple and tough. Heat a cut battery to 120C, and the weight must not decrease by more than 0.5%. Once the standard takes effect, only batteries passing that test can be called "solid state". Nobody has this yet outside of lab samples.

This will help avoid fake solid state battery claims such as the Donut Labs fiasco [2]

[1] https://www.intelligentliving.co/solid-state-battery-standar...

[2] https://www.cnet.com/home/electric-vehicles/donut-lab-solid-...