Cadence function quit working on Garmin Edge 305.

Try this to see if it works...

1. Change the battery in the cadence sensor. (which you did)
   
2. Turned on armin 305 edge outside to acquire satellites (probably not necessary)
   
3. Press reset on the GSC10, and it should flash red and green
   
4. On the Edge unit, go to SYSTEM.
5. Under SYSTEM, scroll to bottom, choose ACCESSORIES.
6. Under ACCESSORIES, scroll to bottom, under Cadence Sensor, to the option RESTART SCAN.
   
7. Press RESTART SCAN.

If that doesn't work, you may have to fiddle around with the sensor. Try moving the GSC10 as close to the crank sensor as possible, then tilt the GSC10 slightly towards the crank. You'll have to forgo using the spoke sensor to determine your speed as it's already calculated by the GPS function.