iPhone battery old, needed replacing
Went very well
Don't just watch the video, important to carefully read the pictures and explanations in the Guide before you begin!
To heat the iphone, I took a sock and filled with a cup of raw rice, secured with a rubber band, then stuck in the microwave for a minute. Nevertheless, the old battery adhesive strips snapped almost immediately. Then I had to use a card to pry the battery off but it took about 5 minutes and the battery came off pretty easily. Just make sure to pry and push (you are pushing away the old adhesive), wedging back and forth, and only from the side of the phone away from the circuit board! Also I stayed clear of the volume controls.
When I got to placing the new battery, the adhesive strips that came with the ifixit new battery were defective/old and did not separate from the blue plastic film. I had to ditch that adhesive and instead used double-sided tape. Otherwise the fix went just as described!