The portable UPB-12K0-2Us dual USB ports provide up to 5V, 1A and 5V, 2A of power, so you can charge two devices at once. Its 12,000mAh capacity charges devices at maximum power up to 4 hours. It protects against short circuits, overvoltage, over-current, overcharges and overdischarges. Charge the Mobile Power Bank by connecting its USB Micro-B port to a USB charger or a computers USB-A port using the included cable. Press the on/off button, and the four LEDs will blink or light solid in various combinations to indicate the battery level.