The OEM battery was starting to rapidly discharge indicating end of useful life.
Even being a tech person all my life, I found that this first time ever iPhone battery replacement a challenge. However, I successfully completed the task.
1) By default, I would not remove the touch screen cables. The replacement of them was the most difficult part of the re-assembly process for me. Instead, I would construct an L-shape jig to support the two halves of the phone to allow for removal of the battery without removing the touch screen cables.
2) Give a strong recomendation to include an additional battery adhesive strip pair. This could have been easily screwed up in the re-assembly process. If this would have happened, I would have been without a phone until a new set arrived.
3) I could have used two removable spacers to be placed at the top and leftside location inside the battery cavity battery in order to allow for easier alignment of the battery as you only get one shot at inserting it due to the adhesive strips. I would have used flat toothpicks or hardboard for this purpose.
4) I used a refrigerator magnet placed inside the battery shipping tray to contain all the small screws.