Applying high concentration (over 90%) isopropyl alcohol to the battery will make the battery removal significantly easier.

Lift the bottom edge of the phone up and hold the phone in a tilted position.

Apply 1-2 drops of isopropyl alcohol into the crevice between the battery and the phone's bottom midframe.

Using too much alcohol can damage the display.

Hold the phone in a tilted position for a minute to allow the isopropyl alcohol to soak into the adhesive.

Alternatively, heat an iOpener and apply it to the right side of the front of the phone for two minutes.