Prepare an iOpener and apply it directly to the battery for at least two minutes. Reheat and reapply the iOpener as needed.

Be careful not to overheat the battery with the iOpener. If you notice the battery swelling at all, immediately remove any heat and let the battery cool down.

Alternatively, apply some isopropyl alcohol under each corner of the battery and allow it to penetrate for several minutes to help weaken the adhesive.