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.