Power Bank Market: By Battery Type (Lithium-Ion (Li-Ion) Battery, Lithium Polymer (Li-Polymer) Battery), By Unit of USB Port (1 USB Port, 2 USB Ports, More than 2 USB Ports), By Indicator (LED Lighting, Digital Display), By Capacity (up to 3,000 mAh, 3,001–8,000 mAh, 8,001–20,000 mAh,