I’m very disappointed about the quality of the battery you sell on your store.
My experience: despite my iPhone 6s was unable to determine the capacity of the iFixit battery, after a year and a half using it the battery itself suddenly seemed to be dead: every time I used to answer an incoming call or launched the camera, the iPhone suddenly shut down. In fact, the maximum capacity of the battery was at a stunning 76% (checked with coconutBattery) — just after a year an half of use! — with the performance of the iPhone halved (checked with Geekbench 5).
Since I “tampered” the iPhone by myself, an Apple PR refused to replace an original battery, therefore I bought another one from a famous online store, paid one third less of the price you ask, and got a battery that almost lets the iPhone determine its capacity — no more Service alert on the Battery Health status.
The only thing I’m satisfied from you is (of course) your exceptional guides and the quality of the tools you provided with the battery.
Portuguese version of the Manifesto already exists: https://www.ifixit.com/Manifesto
To help with your post, I share an ifixit image with a green arrow indicating the rubber you wrote about - http://bit.ly/1V0aOIa