Mice & Trackballs Connect 2 Devices Simultaneously By Bluetooth and 2.4G wirele connection function, can control two devices at the same time, easy to switch Profeional Ergonomic Design With its handy, ergonomic design and high functionality, the vertical mouse is comfortable and supportive for your hand, reducing preure in wrist joint. Comfortable Grip The grip is wider with a gap which makes your hand rest in a more natural way; it doesn't cause as much strain or muscle use to click the buttons. It also has a nice smooth bottom that slides around perfectly on different surfaces. Forward & Backward Button The Forward/backward button provides convenience when web browsing.Note: Forward/Backward button does not work on Mac. 3 adjustable DPI (1000/1600/2400) allows you to easily change the cursor sensitivity according to your activity and track more smoothly on various surfaces for general and gaming needs. 1*AA Battery (NOT included) should last 2-3 months or more for most normal users, it will depend on usage