Repeat this procedure with the adjacent battery cell:

Apply a small amount (about 1 ml) of liquid adhesive remover under the battery cell, and wait 2-3 minutes for it to penetrate and soften the adhesive.

Alternatively, re-heat this section with your iOpener if needed.

Push a plastic card about an inch between the battery cell and the upper case, and slowly pry the cell up to separate all of the adhesive.