Use this guide to revive your iPhone 8’s battery life and performance with a new battery. If your battery is swollen, [[What to do with a swollen battery|take appropriate precautions|new_window=true]].
This guide instructs you to completely 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 the guide, calibrate your newly installed battery: Charge it to 100%, and keep charging it for at least two more hours. Then, use it until it shuts off due to low battery. Finally, charge it uninterrupted to 100%.