Just received my Zanflare F1, and tried charging via USB.
that battery is a working Samsung cell with 3.9something volts.
the led light kept flashing green then red.
according to the instructions it’s either red for charging or green when full.
When you plug the USB cord in and get a flashing red/green, try turning the light on while it is plugged in by pushing the tailcap switch. The light shouldn’t come on, but the red charging indicator should.