Before starting make sure that the mobile is off.

Remove the SIM and SD cards

Hold the screen with the suction cup and use the wide part of the double opening tool to separate the back cover, frame included.

Unplug and set aside the interconnection flex.

Unplug the battery connector.

The battery is glued by two strips of adhesive. They have a small yellow piece to pull laterally and extract the adhesive, however, it is not as easy as it seems. The normal thing is that the adhesive breaks when throwing.

To take off the battery, just pry with the wide part of the opening tool.