Power banks are essential products for our Energy consuming gadgets. It is very difficult to maintain the battery charge throughout the day while using your phone to even half its potential. So, it is important to keep a backup supply always.

In this Instructable, I decided to use my old Laptop battery and make a mobile power bank from the salvaged cells. A Laptop battery needs replacement every few years but all the Li-ion cells inside it are never damaged. They can be extracted and used for various other purposes.

Note: This PowerBank is only capable of charging Android devices. To charge an ios device it needs a special value of voltage (D+ = 2.76v & D- = 2.06v for 1A current draw and d+ = 2.0v & D- = 2.0v for 500mA current draw) at the data pins that can be easily made using a voltage divider circuit with few resistors. But since I needed it for Android devices, so didn't worry much about providing a voltage at data pins.

In case you bought new Li-Ion cells, you can skip this step.

If you are also using an old Laptop battery like me, then you can proceed. The laptop batteries are made up of multiple Li-ion cells connected together in certain combinations. When the battery stops charging or becomes faulty, it has mostly been seen that only a few cells get damaged, whereas all other cells work well. We will use those cells to make a power bank at home.

Carefully open the laptop battery without damaging the cells inside.
Using a wire stripper, cut the solder tabs connecting the cells.
Separate each cell and clean them with a damp cloth to remove the adhesive.
Using a multimeter, check the voltage of each individual cells.
Discard the cells with voltage less than 2.5v as they might be damaged and will be difficult to revive.
I got four perfectly working batteries out of six.

Using Double-sided tape, attach the batteries to the Enclosure Base.
Place the TP4056 charging Module at the designed space and secure it with Double-sided tape.
Similarly, place the 5v boost converter in the designed space and secure it with double-sided tape.
Secure the switch in the slot using Hot Glue.
Refer to the circuit schematic above and connect the components using a Soldering iron.
Before testing the powerbank, it is important to check the output voltage in order to protect your mobile phone from any damage.
Using a multimeter, test the output voltage of the boost converter and regulate it to 5v using the potentiometer knob.
Plug in a USB cable and test the powerbank.
Cut a piece of cardboard piece to cover the box.
Make a slit at the top for the indicator light on the charging module as shown in the image above.
Using Hot glue, seal the box completely.