Apple iMac (21.5-inch and 27-inch, Mid 2011) - Manual (Page 56)

56 Chapter 4 Problem, Meet Solution
Important: If the Apple Hardware Test window doesn’t appear after restarting, hold
down the Command (x), Option, and D keys and restart the computer to access the
Apple Hardware Test software from the Internet. Your computer must be connected to
a network that has access to the Internet.
Replacing the Batteries
Your Apple Wireless Keyboard and Apple Magic Mouse each come with two
AA batteries installed. You can replace them with alkaline, lithium, or rechargeable
AA batteries.
Keep the battery compartment cover and batteries out of the reach of small children.
WARNING: When you replace the batteries, replace them all at the same time. Don’t
mix old batteries with new batteries or mix battery types (for example, don’t mix
alkaline and lithium batteries). Don’t open or puncture the batteries, install them
backwards, or expose them to fire, high temperatures, or water. Keep batteries out of
the reach of children.