About the Apple Remote Control
Many recent Apple computers such as the MacBook, MacBook Pro, Mac mini, and recent iMacs come with an Apple Remote that allows you to remotely control certain features in your applications such as iTunes and DVD Player. The Apple TV also includes an Apple Remote.
AppleTV, Portable Computers, Desktop Computers
About the Apple Remote
The Apple Remote operates on an infrared-based transmitter. If it has an unobstructed line-of-sight to the receiver, the Apple Remote can function at distances of up to 30 feet.
About the battery
The Apple Remote uses a CR2032 coin battery, which is easy to replace. Apple TV or Mac OS X will display a warning icon when the remote's battery gets low. To find out how to replace the battery, see this article.