We used to offer Li-ion AAA batteries. They are currently discontinued, and we do not plan to restock them for the time being. Our stock had a high percentage of defects because of the sensitivity of Li-ion battery chemistry. We found they did not handle the rigors and impacts of spinning as well as we needed them to.
While they work in the flowlight, Li-ion batteries can damage other electronics because they have 3x the voltage of regular AAA batteries. They can even damage a flowlight if inserted in the wrong direction and the button is held down too long! Because of these issues, we stopped offering Li-ions on our site and do not recommend using them with flowlights.
If you need batteries for your lights, we offer NiMH AAA batteries which are optimized for usage in flowlights on our site directly: https://www.flowtoys.com/powerup/batteries/
You are also welcome to use alkaline batteries - though they are not rechargeable - or other high quality rechargeable NiMHs like eneloops.
If you have any questions, please feel free to contact us!