Lift both battery cells out of the iPad at the same time.

Do not reuse the battery after it has been removed, as doing so is a potential safety hazard. Replace it with a new battery.

Remove the old battery adhesive from the frame using tweezers and high-strength (>90%) isopropyl alcohol with a lint-free cloth where needed.

If your battery doesn't come with preinstalled adhesive, use Tesa tape to reattach the battery to the rear case.