Old battery was making phone shut down at 20%
I followed well made instructions exactly and the repair went better than I expected. I replaced old batteries on two iPhones so I bought one repair kit and then just one more battery. I didn't realize that the sticky tape was considered a seperate part so second battery didn't come with the tape. I had to order that separate and wait a few days to do the second replacement, now all is well. My wife tells me that her phone is like new again, so that's all that matters, right? Happy wife, happy life. Thanks, iFixit!
Take your time on removal of sticky tape behind battery. Don't pull too hard. Follow instructions to the letter.