On each side of the battery there are 2 holes. Line up the holes with the gold plated screw port threads and black notches underneath them. See video.

Make sure the battery lies flat and secure within the bay before replacing the bottom cover/shell.

When maneuvering the battery back into place, keep an eye on the speaker wires that cross over the top right corner of the battery. These wires can get stuck behind the battery which therefore may not allow the battery to sit flat and secure in the bay. Makes sure the battery sits underneath the speaker wires.