Two possibilities I know of, second one is like @FriedCheese2006's recommendation:
- Centralite 3420 Nightlight Repeater with Battery (https://www.centralite.com/downloads/DataSheet-3SeriesNightLightRepeater.pdf)
If you are just looking for on/off/dimming level... it works great. You can even MANUALLY set the color if you do not want just white. It was very frustrating that it did not work as they SAID it should (and they STILL have not corrected the DataSheet I linked)... both @bcopeland and I wrote drivers for it... for what it can do. Here is the link for that thread. But if it's limitations are OK, then it works. - Like @FriedCheese2006, I would recommend a ZigBee RGBW device that can be powered by USB. I use a GLEDOPTO model (https://www.amazon.com/GLEDOPTO-Zigbee-RGBCCT-Compatible-Control/dp/B08FC6ZSF4?th=1) that is RGBCCT (so you get a wide color and white spectrum) and just have it on a USB battery. They come as a 2M (6ft) LED strip but you could cut it, coil it, however you want.
