Remove the battery.

To install a replacement battery:

Remove any battery adhesive remaining on the phone.

Install replacement pull-stretch adhesives, or double-sided tape such as Tesa tape, in the phone's battery well where the original adhesive used to stick.

Gently set the battery in place. Temporarily connect the battery's connector to the motherboard to ensure that the battery is properly positioned.

Press the battery firmly in place with your fingers.

Disconnect the battery from the motherboard and resume re-assembly.