BUILT-IN BATTERY:2.4 GHz wireless mouse,built-in battery,easy to charge by micro usb cable,no more need for extra AAA battery.Note:USB Nano Receiver is stored within the back of the mouse.Please keep the mouse power switch in "ON" position when charging . WIDE COMPATIBILITY:Compatible with most system including Windows, Mac and Linux. Fit for Notebook, PC, Laptop, Computer, Macbook and other device with USB interface. 3 DPI SWITCH:Using high-performance optical chips, up to 1600 dpi(800, 1200, 1600), can be applicable to all kinds of games, accurately tracking AUTO ENERGY-SAVINGSLEEPING MODE: Li-polymer batteries,high cycle life.the Auto Switch Off function will help you save energy as your Wireless Mouse will switch off when your PC is turned off or the receiver is disconnected. If you do not use the mouse for eight minutes, it will go to sleeping mode, you can press the any button to wake it up.