UPDATE...
I installed the iFixit replacement battery yesterday. It made a measurable improvement in my phone's CPU Geekbench scores. (See before and after scores below) In addition to that, I hope that the new battery won't mysteriously discharge in rapid fashion like its predecessor. Recently, the old battery went from fully charged (100%) to 64% in less than an hour, to 24% minutes later. This is despite the fact that the battery had less than 250 charge cycles and a capacity of 84% of its designed capacity. In other words, my old battery would pass Apple's diagnostic test.
Having replaced the battery myself, I do
not recommend most people attempt it. The procedure is simple. You remove a half dozen screws and break the adhesives attaching the display and battery. However, you must be patient and prepared to solve some of the potential issues that can arise. For example, the adhesives didn't give; I had to use a hairdryer to soften them. Furthermore, you need good eyesight and a steady hand; the screws are as small as gnats (no exaggeration). What was described as a 20 minute task took me 2+ hours!
P.S. The old battery's Geekbench test was performed when the battery was fully charged. The replacement battery's test was performed while it had only a 50% charge (they arrive only partially charged).
View attachment 746700 View attachment 746704