This listing is for an official Nintendo licensed watch. Guaranteed works! This watch is brand new still in the original package. It uses one U.C.C. 392 or equivalent battery. The original battery has died, we will include a brand new battery for free. You just need a small screw-driver to change the battery. If you want us to change the battery for you, please leave a message before we ship it out, we will open the original package and change it for you at no extra charge. Here is how to change the battery: Use a small screwdriver. Take out the battery, then press down the metal that holding the battery. Then put back the battery. Try let the metal touch the battery as much as possible.