The Sleek Aluminum 4,000 mAh Power Bank is a rechargeable lithium polymer Grade A battery device with a total output of 5V/2A. The dual output allows you to charge two devices simultaneously. It also includes a battery check button to ensure that you know how much battery life you have left. The reusable power bank charges via a USB cable (included) which can recharge the battery backup or be used to charge devices with a micro-USB input. Logo is laser engraved.