The time and date, as well as other settings, are kept by the PRAM battery when your machine is off.
Turn the computer so that the ports are facing you.
If the keyboard is locked, open the port cover and turn the keyboard locking screw until the keyboard is unlocked.
Pull the keyboard release tabs toward you and lift up on the keyboard until it pops free.
Lift the keyboard out by pulling it up and away from you. Rest the keyboard, face down, on top of the trackpad.
Pull the battery cable directly up from the logic board.
Remove the battery from its holder by pulling up and to the left.