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.
thegearlife - Garmin HRM-tri In-Depth Review
Garmin HRM-Swim Heart Rate Monitor
Garmin HRM-DUAL Heart Rate Strap In-Depth Review | DC Rainmaker
Garmin HRM-PRO Review & Discounts
How long do HRM-Tri batteries last? – Chris Worfolk's Blog
Forerunner 920XT - Replacing the HRM-Swim Battery and the HRM-Tri Battery