Removed old battery, and replaced with new one. iFixit tools were the easiest part of the problem. The hard part was removing the adhesive taped battery from the inside of the laptop.
To do that, I saw some recommendations of using rubbing alcohol, to minimize problems with the adhesives. This helped a little, but it took more effort. There is also the concern of the alcohol dripping into other circuits and components; so, be careful! Using the alcohol also takes time to "melt" the glue.
Now the secret to my effort, after pried the battery cells with a screw driver and a spudger, I decided I needed to get behind the glued area. To do that, I looked for a long piece of string; and wrapped it behind one of the battery cells. Then pulled the string down behind the cell, to break the backing and glue. While this took a LOT of pulling, it worked very well. I really don't think I could have done it any other way. It took a lot of patience and a blistered finger; but it worked.
Most resources I used were a couple online videos; but the biggest help was here on iFixIt. I took two hours to complete.
I am pleased with the results. The battery is up and running. The only downside is the new battery did not have adhesive, causing a slight rattle, inside the housing; however, this is so minor. The positive aspect of not having glue on the new battery, it will be much easier to replace the next battery!
Try using string behind the battery, and pull. Old fashioned toolbox tools are too rough to use on the sensitive machine. Some online resources say there are toxic gases that can be expelled, if the battery is punctured; and I did see some "smoke" when I poked one of them too hard.
Add a syringe to your tool list, it would be helpful to apply the rubbing alcohol. I used a straw, from the kitchen drawer; and it was a little too wide.
Keep track of the screws. They are all small, but two of them are SLIGHTLY smaller. There are two larger battery cells in the center, and they lay under the trackpad; so be careful handing the "plate" that is under it. The other cells are mounted to the inside of the case; and there are no major concerns or sensitive elements. However, many components are closely integrated; so carefully consider prying against too many surfaces.
- P5 Pentalobe five-point screwdriver for the outside case
- T5 six-point screwdriver, to take out the two battery screws.
Bottom line, take your time and go slow. No reason to take your machine to the Geniuses, pay a lot of money and give up your computer for two weeks in the repair shop. Good luck.