LG MM-535 Owner's Manual page 27

Insert the battery (label side facing up) into the cavity at a
45-degree angle. (The metal contacts must be aligned with and
touching the metal prongs.)
Press down on the battery until it snaps into place.
Make sure the power is off so that you don't lose any stored
numbers or messages.
To remove the back cover, turn the phone upside down, press
the release button down, and push the back cover away.
Pull downward on the upper end of the battery with your finger
tip and remove the battery from the phone at a 45-degree angle.