Remove the battery.

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

To install a new battery:

Remove any remaining adhesive from the battery well.

If your replacement battery does not come with replacement adhesive, lay some double-sided tape or pre-cut adhesive strips in the headphone's battery well.

Peel away any tape liners to expose the adhesive.

Lay the battery on the adhesive and press firmly.