These are very slim, extremely light weight batteries based on the new Polymer Lithium Ion chemistry. This is the highest energy density currently in production.Do not attempt to charge these with anything but a specialized Lithium Polymer charger. All the smart phones, Tablets and even wearable uses this type of batteries.
DC – DC Boost Convertor Module
TP4056 Lithium Polymer battery charger module
The TP4056 IC is a complete constant current/constant-voltage linear charger for single cell lithium-ion/Lithium Polymer (LiIon/LiPo) batteries. Its SOP-8 package and low external component count make the TP4056 ideally suited for portable applications.Furthermore, the TP4056 can work within USB and wall adapter. Other features include current monitor,under voltage lockout, automatic recharge, and two status pin to indicate battery charging(RED LED), and full charged battery (BLUE LED).
Note:It is preferred to use this type of specialized charger rather than any 5V charger otherwise it may harm the battery.
This is the link from where I have ordered this module:
This is all you need for making your own power bank. If you still not cleared about this, just watch the video of Making your own POWER BANK” whose link is mentioned below.