This guide instructs you to fully detach the display assembly; this is intended to prevent accidental damage to the display cables. If you feel comfortable removing the battery without putting undue strain on the display cables, you can skip the steps for detaching the display. Additionally, while it’s possible to remove the adhesive strips securing the battery as soon as you open the phone, this guide recommends first removing the Taptic Engine. Doing so reduces the risk of breaking the lower adhesive strips accidentally, either by snagging them on the Taptic Engine, or by pulling the strips at too sharp of an angle.
For optimal performance after completing this guide, calibrate your newly installed battery: Drain it below 10%, then charge it uninterrupted to 100%.
Opening the iPhone 8 will damage the waterproof seals on the display. If you do not replace the adhesive seals, your phone will function normally, but will no longer be water-resistant.