the O-ring around the battery deforms plastically (i.e. it's not flexible enough to return to it's originally formed shape, which causes flat spots on the seal allowing for moisture to enter and causes the HRM to fail)
Hairline Crack video: • Garmin HRM Tri stopped working (Why and ho...
HRM Swim with cracks in the casing: • Garmin HRM Swim casing cracked after batte...