0537 is the model number for a heart rate wrist monitor made by Polar Electro, more commonly known as Polar. The average life of a Polar wrist monitor battery is one to two years, although the manufacturer warns that you shorten the life of the battery the more you use the back light and the audible alarm. When the battery becomes low, a low battery indicator appears on the screen prompting you to remove the old battery.
Set a coin in the slot on the back of the wrist monitor. Turn the coin counterclockwise to open the battery compartment.
Pull the battery cover off the back of the wrist monitor.
Use a toothpick to gently pry up and remove the old battery.