Return all 3 batteries back into their correct places.

Make sure the positive ends on the batteries are aligned opposite the springs and the negative ends are aligned to the springs for correct electrical connectivity.

Place the plastic cover over the box and slide it down until it snaps closed with your thumbs.

After this step, the repair is done. Try turning the on switch of your lights, and test out your working lights.

If the lights are still lagging or not lighting, double-check if the batteries are placed in their correct placements. Another option is to follow steps 1 through 6 again.