Looking at the disc from the underside, assure that the post on the bottom of the disc is aligned with the two pegs on the cap. Having the cap turned to the "off" position is helpful.
 Grip your thumb under the scalloped edge of the battery cap and pry the cap off with your thumb.
 Peel the cap off and set it aside exposing the inside of the battery compartment.
 The battery will be nested in the battery compartment with the [+] positive side up.
 For a reference, this picture illustrates how the inside of the battery compartment should look like without the battery. The LED is snapped down inside the disc with the two LED leads; [+] and [-] bent into their respective locations.
 Place you new battery in the battery compartment with the [+] positive side up.
 Re-align the pegs on the battery cap with the post on the disc as you did when you peeled the battery cap off (see figure 1).
 Firmly snap the cap back down in a flush postion to the disc. Resume play.