The bigger of the two solar panels on the Amazfit T-Rex Dual Solar sits against your wrist.
Zepp Health is building the watch with photovoltaic surfaces, panels that turn light into electricity, on both the face and the case back. The latest build of its companion app describes both of them plainly, and gives each one its own charging measurement. Marko Maslakovic at Gadgets & Wearables pulled the description out of the app package, the file an Android app ships in, and his is the only account of it so far.
That is a strange watch to build. Solar wearables normally put all of their light gathering into a ring around the display, because the display is the part of a watch that sees the sky while you are wearing it. The back of a watch sees a forearm.
So the larger panel only works when the watch is off.
Zepp Health has also written a way to show what each surface is getting. The Solar Charging Index reports a separate figure for the face and for the case back, rather than putting a sun icon on the screen and leaving it there. Its reference point is 50 kLux, a measure of how bright the light landing on the panel is, and Zepp Health calls that reading 100% for the watch face. The number is not a charging rate and not a battery level. Under the same light the case back should report a higher figure, because it has more panel to report about.
Two other pieces of the system sit better next to this. Solar Boost Mode turned up on the same teardown trail last month. It strips the watch back to the time, the battery level and the solar readings and switches off much of what else it does, so less power is going out while the panels bring power in. Charging also pauses when the watch gets too hot, which matters if the way you use that rear panel is to leave the watch lying in direct sun.
The watch keeps separate statistics for both charging surfaces, so an owner can tilt it or turn it over and see the index answer. That is a long way from the passive top-up most solar watches offer, where the only thing you can do about the sun is stand in it.
Zepp doesn't have much of the year left to ship it. On the second-quarter earnings call, CFO Leon Deng said the company was almost done with new product launches for 2026 and put what was left at one or two products. Regulatory filings have tied model number A2570 to this watch. There is still no launch date.