Edge 820 - Replacing the Speed Sensor or Cadence Sensor Battery
Original Replacement Battery For Garmin Edge820 Edge 520 Plus Edge 500 205 200 Edge 820 520 GPS Cycling Computer 361-00043-00 - AliExpress
Amazon.com: NP99sp NewPower99 Battery Kit for Garmin Edge 820 and Garmin Edge Explore 820 with Tools, Video Instructions, Long Life Battery : Electronics
Rear Housing Assembly With External Side Buttons & Battery for Garmin Edge 820