This 4,000 mAh rechargeable lithium polymer Grade A battery device is enough to charge smartphones, MP3 players and tablets with a total max output of 5V/2.1A. The dual output allows you to charge two devices simultaneously. It also includes a battery check button, making sure you know how much battery life you have left. Reusable power bank charges via USB cable (included) which can recharge the battery backup or be used to charge up devices with a micro-USB input like Android smartphones from Samsung®, Motorola®, HTC®, Nokia®, and others. Input 5V 1000mA. Output 1:5V 2100mA/Output 2:5V 1000mA.