I'm using thermoelectric module to get the voltage. With the help of it, I'm getting 3 volts Open circuit voltage. I've attached DC-DC converter which regulates this voltage to 5 volts. I've attached USB at the output of the converter to connect my phone for charging. The thing is a basic cell phone is getting charged some 20% and then it doesn't progress even after 2 to 3 hours of connecting to USB. And whenever I connect smartphone, for a second charging symbol pops up and then charging stops.
Then the phone charge circuit is not measuring enough capacity of either voltage or current to stay engaged.
Solution is to make sure that the voltage does not drop under load and that sufficient current is available. Some phones need to see 2A available, but will only use what they need of that.