LunaR has two stages of (solar) charging:
In the first stage (with less sunlight) the energy gathered by the solar panel supports (or takes over) the function of the battery. The smart functions of LunaR (like the LED's and the bluetooth) are (partly) powered by the solar panel.
If you have opened the App and synced the data a lot; if you have set notifications for different Apps and receive notifications a lot; and the alarms; those are all the factors that will consume the battery really fast.
In the second stage, with more sunlight, the solar panel can harvest enough electricity to serve the smart functions and to charge the battery that's inside LunaR.
To trigger the solar charging, it will need a little power from the battery, so LunaR can't be charged when the battery level is extremely low.
So if you have seen no changes on battery level, please check if the watch face has been covered by your sleeve, or maybe the light intensity did not reach 10K Lux, or that amount of electricity that's harvested has been used.
But even with that, LunaR can be used for months without charging.