This guide will teach you how to replace/install the battery.
Place the device on a flat surface (with the headphone outlet facing you). Using one of your fingers, place the tip of your finger over the highlighted spot (as shown in the second picture). Next, pull the back cover upwards.
If the first method is too difficult, use the plastic opening tool in order to complete this step. Stick the plastic opening tool inside of the gap. (The gap is located on the top of the device which is highlighted in the second photo). Using the plastic opening tool pull the back cover upwards until the back cover pops off.
Lay the device on a flat surface with the screen facing downward. Use one hand to hold the device down in place. With your free hand use one of your fingers and stick it in the gap (as highlighted in the photo)and pull it up towards you.
The gap is located on the left side of the device in the upper left hand corner and the on the right side of the device in the upper right hand corner.
If the battery is not coming out with this technique, use the plastic opening tool to stick it in the gap and pry it up towards you.
The battery will pop out.