Insert the flat side of the standard spudger underneath the battery and use a prying action to loosen the glue holding it to the digitizer.

Do this all around the battery until it comes off.

The glue is strong, so some force may be required. However, be careful not to apply so much pressure that the battery bends or breaks.

At this point, do not attempt to fully remove the battery, since it is still connected to the motherboard.