Here is a “Green Project” for you to reuse the discarded Mobile phone battery. When I purchased a new Mobile phone, the old one became junk. But it has a very good high efficiency and long lasting Lithium Ion battery rated 3.7 V, 1800 mAh. So I decided to reuse the battery for an alternate purpose. A simple power supply with DC- DC Booster capacity and a White LED emergency light. It can be charged from any USB charger or Laptop. Its output can be adjusted from 3.7V to 37 volts. The DC-DC Booster module boosts 3.7V from the Mobile battery up to 37 volts when turning the pot. The Power supply unit is ideal to power all projects that require 3.7 V to 37V. Its emergency light helps to do work in low light conditions. You have a number of Mobile battery in your Junk box. So try this Green project .It is a worth.
See block diagram. Connect accordingly.
Take two USB Cables and cut to take the USB connectors . Join both with correct polarity ( Red-Red, Black – Black wires). So both the sides will have USB connectors . One end can be connected to the power supply unit and the other end to the charger.
You can adjust the preset of the DC-DC Booster Module to get 3.7V to 37 V output. The battery backup depends on the capacity of the battery using. Here 1800 mAh battery is used. It can give 1.8 Amps in one hour. You can charge the battery using any USB type charger. Insert the USB pin into the socket. The 5V DC from the charger will charge the battery. From the USB socket, the 3.7V can be obtained for powering projects that requires low voltage. If you need more voltage, use the out from the DC socket. The preset can be adjusted to get 3.7V to 37 volts.