I’m counting the parts which I didn’t replace in my old 2012 retina macbook pro. It’s not that I wouldn’t like to fix things, but my keyboard, speakers, batteries, and two magsafe cables is a little bit much.

Anyway, I bought an Ifixit repair kit, and it worked fine. They sent all the tools i needed to do the replacement.
They also have a repair guide which is very clear. A few notes I would add.

• drain your old batteries fully to prevent any fire caused by physical impact while removing the old battery
• you dont need to cover your screen if you place your computer on the edge of the desk, hanging the screen down.
• be careful with the glue stripes, you cannot move the batteries if they stuck on the top case.
• After the installation, the measured capacity changed erratically. Don’t worry, just keep doing recalibration a couple of times, and it will work correctly.