Don't trash your perfectly good laptop—replace the battery!
Il Mio Problema
After 1,000 charge cycles on my 2012 Retina Macbook Pro, my battery had hit the skids. Furthermore, I'd cracked the trackpad and purchased a replacement. After realizing I'd need to remove the battery to do that repair, I just waited until the battery was ready to go...
La Mia Riparazione
It's brutal. None of is iFixit's fault! If anything, they are helping our planet. There is NOTHING otherwise wrong with a six-year-old fast MacBook Pro, and the design Apple chose for the battery (to glue it to the case with industrial epoxy) is the opposite of sustainable! I've enjoyed Apple products for years, but the gymnastics they put one through to replace a battery seems absurd at best to me, and profit-motivated at worst. I LOVED the iFixit kit because it truly has everything you need, and the tools are yours to keep forever for future repairs. They did all the work of thinking it through—you just need to follow the directions and you will get it done.
Il Mio Consiglio
Allow yourself time to go slowly and carefully! Do not hurry in removing the very fragile connectors inside of your Mac—just take time to be careful with them. SEPARATE THE SCREWS for each part and find a way to keep track of them. If you end up with a pile of silver and black screws all together, you will struggle in getting it put back together correctly. (A lot of the screws LOOK the same but are in fact slightly different.) On that note, maybe don't do the repair while your six-year-old boy decides to play with the screws and knock them on the floor ;)