A:Answer It doesn't use batteries. It is rechargeable. You plug a cable in to the front of it for a while, it charges up. If you look at settings in the Bluetooth section, it will tell you what percentage charge it is at currently. I just checked mine, it is now down to 20%, so I need to plug in the cable. I can still use the mouse while it is charging. The same cable will also plug into the keyboard to recharge that.
My wife has an Apple computer, with a rechargeable mouse. She gets annoyed with it, because the recharge connection is on the bottom of the mouse, not the front end like the Logitech mouse.