Power bank is an external charger for charging mobile phones and other electronic devices. It is serve as an extra battery , a portable device that can supply power from its built-in batteries through a USB port. They usually recharge with USB power supply. Technically, a powerbank consists of rechargeable Lithium-ion or Lithium Polymer batteries installed in a protective casing, guided by a printed circuit board which ensures various protective and safety measures. In power bank the number are indicate from total battery cell capacity. More cell means more power that can be save and ready for backup your device. Majority of the power banks in the market are actually made in China.