As you work, try not to accidentally power on the phone. If you do, turn the phone off before resuming disassembly.
Place a suction cup near the bottom edge of the display.
Pull on the suction cup with strong steady force.
Press the edge of an opening tool straight into the frame seam near the suction cup until the edge wedges between the plastic frame and the back cover's lip.
Due to tight tolerances, this will take substantial force. Using a new opening tool with an unmarred edge will help with this step.
Do not use metal tools, as they will most likely crack the screen.
Continue sliding the opening tool along the long edge, releasing the clips along the way.
The last clip in the top-left corner near the alert switch is recessed and can be difficult to release. Take your time and use the flat end of a spudger or an opening pick to help.
Carefully bend the still-attached daughterboard flex cable away from the battery.
During reassembly, make sure that the Main labeled connector connects to the motherboard. The Sub connector will fit the motherboard socket but it will cause your phone to malfunction.
Use the opening tool to push any adhesive tape holding the battery to the edge of the plastic frame. There should be at least one on each battery side.
Be careful not to puncture the battery pack with the tool.
Remove the battery and any remaining adhesive residue on the frame.
Do not reuse the battery after it has been removed. Reusing a battery that is bent or otherwise stressed is a potential safety hazard.
If your replacement battery did not come with a pull tab, you can transfer the old tab to the new battery to help with subsequent replacements.
While installing a new battery, temporarily connect the battery to the phone to ensure proper battery alignment.
To install a new battery onto an existing frame, remove some adhesive strips from a pre-cut adhesive card, or cut some strips from a roll of Tesa tape, and stick them in the highlighted area.
If you are installing a battery onto a new screen and digitizer assembly, be sure to peel off the orange adhesive liner to expose the battery adhesive for the new battery.
The tutorial for the 3T model would be similar, but not completely identical to this guide. Since the battery capacity is different between the 3 and 3T, the repair kit would not be applicable. However, the tools are most likely the same.
Thanks for your response Arthur! Is it planned to offer a battery kit also for the OnePlus 3T? I’d definitely appreciate it since I can’t find any trustworthy OnePlus 3T batteries so far. Best regards!