INTEGRATED MONITORING CHARGING EFFICIENCY OF A RECHARGEABLE DEVICE VIA A POWER BANK

A portable power bank for charging a rechargeable device is described, and a dynamic charging efficiency is monitored while the power bank is charging the rechargeable device. Particularly, instantaneous power output of a battery of the power bank is compared to power received by a battery of the rechargeable device to determine efficiency. The charging of the rechargeable device by the power bank is interrupted and/or resumed based upon the charging efficiency at any given time, thereby preventing inefficient use of the power bank.