Apple MacBook Pro (15-inch, Late 2008) - Manual (Page 29)

Chapter 2 Life with Your MacBook Pro 29
You can also check the amount of battery charge remaining by viewing the Battery
( ) status icon in the menu bar. The battery charge level displayed is based on the
amount of power left in the battery with the applications, peripheral devices, and
system settings you are currently using. To conserve battery power, close applications
and disconnect peripheral devices not in use, and adjust your Energy Saver settings.
For more information about battery conservation and performance tips, go to
www.apple.com/batteries/notebooks.html.
Charging the Battery
When the power adapter that came with your MacBook Pro is connected, the battery
charges whether the computer is on, off, or in sleep. The battery charges more quickly,
however, if the computer is off or in sleep.