I’ve changed my Polar battery multiple times. The price Polar charges for a battery change is a complete rip off. It’s such a scam. Almost as bad as paying so much for razor blades.

1. Thoroughly clean your watch before taking it apart.
2. Remove the screws (small, easy to lose)
3. Separate the two halves and carefully remove the gasket from its channel
   
4. The battery should now be visible. Mine is model CR2354 and can be purchased for under $10.
   

   NOTE: This is an electronic device so be very careful not to discharge any static while touching the interior.

5. While you have the case apart clean out any dust or grit that has collected near and in the channel that the gasket fits within.
   
6. Clean the gasket with a little bit of water and dish soap. Allow time to dry.
7. Replace the battery (you should see the watch display reset)
8. When the gasket is dry, place it back into the channel on one half of the body.
9. Place the two halves back together. Take care that the gasket seats correctly and you don’t pinch it.
10. Insert the screws and begin tightening in a balanced rotation, similar to how you would tighten lugnuts. If you tighten only one at a time you may create a pinch point which can cause a leak. Also, don’t over tighten. How tight you ask? Sorry, I do it by feel. Just realize you aren’t trying to lock down a disc rotor.
    

You should now have a happy full of juice Polar.

Now go ride!

Cheers!