How to Replace the Battery in a Polar CS Speed/Cadence Sensor
By Brian Lewis
I got really tired of buying $33 Speed and Cadence sensors every 6 months for my CS300 Polar Watch. The 4500 hour rating for these sensors is a joke, you'll never achieve anything close to that.
Since I had 2 sensors that were nearly dead (1 ft range only) I decided to attempt to take them apart. I used a new single edge blade (MUST BE NEW AND SHARP) to cut along the edge of the casing where the two halves meet. I started at the corners first which was easiest to press in, then once the edges were completed I would cut from edge to edge with the razor. This is why it must be a brand new razor, you are attempting to cut the plastic that is part of one of the halves. The units clamshell together, with a little glue, one side having a groove, the other side having a matching plastic lip. You are cutting this lip around the sensor with a razor to separate the clamshell. Once you get an edge and part of a side cut you can use a small flathead to pry it slightly while you continue cutting, sometimes it will just let you pry the rest up out of the groove, so really you might only need to cut half of the shell. Inside will be the board and a CR2032 battery. Replace the battery with a new Duracell unit from your local grocery store. Home Depot has them as well. Mix up some 5 minute epoxy on a piece of cardboard with a screw or other disposable stick, then lightly wipe along the edge of one side and put the clam back together. I then use a large black binder clip to hold the pieces together until the glue is completely dry (1-2 hours)
