Armitron sport watches are multifunctional wristwatches designed for durability. Many come with an outer guard that protects the watch face and many include features such as a stopwatch that can be used during your exercise routine. Many of these watches are also waterproof. However, you can't use any of the features without a good battery in the watch. Unlike many other brands of wristwatch you don't have to take the watch to the manufacturer in order to have the battery replaced.

Take your armitron watch off and place it face down so that you have access to the back panel of the watch.

Insert the tip of a thin blade into the seam where the back plate meets the body of the watch. The type of blade on a Swiss army knife is ideal for this purpose.

Pry the blade up to pop the back case off of the unit. The small circular battery will now be visible. It is held in place with a thin latch. Note which side of the battery (+ or -) is facing up, as you will have to insert the new battery the same way.

Use the tip of a small screwdriver to move the latch off of the battery. Use the tip of the screwdriver to pop the battery out of the watch and set it aside.

Fit a new battery in the watch and slide the latch into place.

Fit the back case over the rear of the watch and push it firmly down until it is secured.