Apple TV (3rd generation) - Manual (Page 23)

Chapter 3 Watch. 23 Chapter 3 Watch.
Changing the remote battery
When the battery charge in your Apple Remote is low, Apple TV displays a
picture of a remote and a warning symbol (·). Replace the battery with a
CR2032 battery.
Battery
compartment
To replace the battery:
1 Use a coin to remove the battery compartment cover.
2 Remove the battery.
3 Insert a CR2032 battery with the positive side (∂) facing up.
4 Replace the battery compartment cover and use a coin to tighten it.
Important: Dispose of the used battery according to your local environmental
laws and guidelines.