I've put the device attached at a solar cell with 5V under full sunlight, a LiPo (2000mAh) and a LED (10mA) as load at the 3V3 output. Everything worked fine and the would be loaded slowly (not always sunny) from 3.9V to 4.2V. But immediately when the battery was fully loaded the output voltage begans to fluctuate at 2.7V (DMM measurement) and as a result the LED blinks. I attached some big capacitors (2 x 470uF) at Vout, but it was not possilbe to flatten the fluctuation. Also shadowing the solar cell (output down to 3V) does not help
With that result the product is unusable
If there is any improvent I can do, please let me know
Input voltage should be kept below 4.2V. It is a boost converter on the input. Not all input voltage / battery type combinations work well. Some input voltage tweaking might be necessary for optimal results. Try with 1V on the input, that might yield cleaner output voltage.