All watches use a button cell battery, but the voltage and size code number vary by model. If the voltage and size are not inscribed on the back of the watch, take the battery out to verify its details.
To take your watch apart, determine whether it is a screw-back, hatch-back or snap-back watch. Screw-back watches typically require use of a special tool, while hatch-backs can be taken off with tweezers and snap-backs can be removed with a penknife. Check the code number for your exact size and voltage to determine the battery you require. If you rarely need to use the tools for this, it is recommended that you consult with a professional to change the battery or check its voltage.