Garmin Heart Rate Monitor Not Reporting Accurate HR Anymore
Given the battery changes, if you haven't washed the strap, try doing that, first with soap and water, then wipe with isopropyl alcohol. If you get no different response, replace the strap. BTW, I recently had to replace my Edge 305 because the PC drivers were blue screening my Win 7 PC. If you use the Garmin software at all, you might consider an overall upgrade. In addition, they've changed the design f the Garmin HR strap, so if you do decide to replace it, it will be with the newer soft strap, not the same as your original one.