Wearing a necklace watch is a stylish alternative to wearing the classic wrist watch, but just like a wrist watch, eventually you will need to replace the battery. Replacing the battery yourself doesn't need to be a hard task, as long as you have the right tools to do the job. If your necklace watch is made of a high-percentage of a precious metal, you will need to take special care not to scratch the metal--as precious metals tend to be softer.
Place your watch necklace face down on a clean, soft cloth or piece of material. This is to protect the watch face from getting scratched on your work surface.
Use a watch case opener or other tool to open the back of the necklace watch. A watch case opener has a knife-like edge, so you can also use a small knife or any other object similar in shape. Use the cloth to cover your finger as you grip the watch with one hand. Find the indent or groove in the back of the watch and gently wedge the edge of the opener tool into the indent.
Twist up and down, and pry the back off very carefully. You do not want to scratch the metal and you also do not want to stab yourself with the tool, so work slowly at removing the back panel.
Take note as to which end of the battery is facing up and remove the old battery. The battery is held in place by a metal clip, so use plastic tweezers to pop the battery out. Use a jeweler's screwdriver to remove the clip if the battery is held in place by a screw-on clip.
Check what specific kind of battery your watch requires. It will have a series of numbers and letters, and a brand name on it. The brand name doesn't need to match the replacement battery. Purchase a new battery with the same code on it.
Snap the new battery into place with the correct end facing up--and replace the screw-on clip if necessary. Align the rubber gasket on the inside back panel with the inside gasket of the opening and apply pressure to snap the panel back on. Your necklace watch should now be ticking again and ready to wear.