After a couple minutes, insert one corner of a plastic card underneath the battery, starting from the lower edge of the bottom, right-most cell.

Wiggle the card from side to side and slide it all the way underneath both battery cells.

Lift the cells to fully separate the adhesive, but don't try to remove them from your MacBook yet.

Leave the plastic card temporarily underneath the cells to prevent the adhesive from re-bonding as you proceed to the next step.