There are three notches on either side of the battery. In the next few steps, you will be using these notches to gradually pry the battery up from the rear case.

The battery is secured with large amounts of adhesive, so you'll need to go slowly and carefully to avoid puncturing or creasing the battery.

Insert a plastic opening tool into the top right notch and gently pry up on the battery.

Do not attempt to pry up the entire battery at this point; you just want to start to loosen the adhesive at each of the prying points, in turn.