To increase your odds of success:

Don't press down on the battery. Hold the iPhone firmly by its sides.

Keep the strips flat and unwrinkled as you pull.

Pull very slowly, giving the strip time to stretch and separate. It takes around 30 seconds of stretching to remove each strip.

Pull at a low angle so the strip doesn't snag along the bottom edge of the battery.

If a strip does break off underneath the battery and cannot be retrieved, move on to the other strips and then continue with the additional steps below.