Mac OS X 10.6: Replacing Apple wireless mouse batteries
When the batteries in your Apple wireless mouse need to be replaced, replace all of them at the same time with the same kind of batteries. The Apple wireless mouse uses two AA batteries. Make sure the positive ends of the batteries are pointing the correct direction.
The Apple wireless mouse comes with two nonrechargeable AA batteries. You can also use alkaline or rechargeable AA batteries. Dispose of batteries according to local laws and regulations.
To replace the batteries of an Apple wireless mouse:
Turn over the mouse.
Remove the battery compartment cover and insert two AA batteries. Make sure the positive and negative ends are facing the correct direction.
Replace the battery compartment cover.
If you’ve previously paired your mouse with your computer, you do not have to set up the mouse again after replacing the batteries. The mouse should automatically pair itself with the computer a few moments after you turn it on.
If you have never paired your mouse with your computer, you’ll need to do that before you can use it. See the documentation that came with your mouse, or search Mac Help for setting up a wireless mouse.