Most of the Mobile Phones battery are rated 3.6 volts at 1000 to 1300 mAh. These battery sets have 3 Lithium cells which have 1.2 volt rating.
Typically a battery pack sufficiently requires 4.5 volts and 300-500 mA current for fast charging. But low current charging is preferred to increase the efficiency of the battery. The mobile phone charger circuit based project described here provides 4.7 V of the regulated voltage and a sufficient amount of current for the slow charging of the mobile phones. Regulated output is given by the transistor T1, output voltage is controlled by Zener diode ZD and the polarity of the output supply is protected by D1. Front end of the circuit should be connected to an A type USB plug, a red wire to pin1 and black wire to pin 4 of the plug for easy polarity recognition. The output of a suitable charger pin should be connected with the mobile phone. After the circuit is assembled, USB plug should be inserted into the socket and output should be measured from the circuit. If the output is OK and polarity is correct, connect it with the mobile phone and if the polarity is incorrect, it will destroy the mobile battery so extreme care should be taken.
For making this mobile charger circuit, a USB cable is used with at least one male plug on it and strip back about 5 cm of the outer insulation with shield from the bare end of the USB cable. Normally, USB cables have four wires i.e. red, green, white and black. As green and white carry the data so they can be trimmed as they have no use here.. Mostly black wire is NEGATIVE and red is POSITIVE. The voltage across USB is about 5V with 500 mA as maximum current for any device. Now power lines are connected to the USB plug with correct polarity. Reflectors are used for LEDs to get maximum illumination.