Garmin Fenix 3 - Garmin: Replacing the Battery in your Heart Rate Monitor ( HRM) The CR2032 batteries in your HRM-Run, HRM-Swim or HRM-Tri straps will last approximately 18 months, depending on use.
HRM-Pro Plus Owners Manual - Replacing the Heart Rate Monitor Battery
Garmin HRM-Swim Heart Rate Monitor
Battery Replacement Instructions for Premium Feature HRM Straps | Garmin Customer Support
HRM-Pro-battery-replacement - OneManEngine
Garmin Forerunner 630 In-Depth Review | DC Rainmaker