How long do HRM-Tri batteries last? – Chris Worfolk's Blog
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-PRO, Premium Heart Rate Strap, Real-Time Heart Rate Data and Running Dynamics, 010-
HRM-Pro Plus Owners Manual - Replacing the Heart Rate Monitor Battery