Garmin HRM 200
It runs up to 12 months on a CR2032 at 1 h a day. Its page lists heart rate and HRV only, with no running dynamics or stored sessions.
What the maker states
| Battery | 12 months, CR2032, using 1 hour per day |
|---|---|
| Weight | 56 g, With XS-S strap; 63 g with M-XL strap; module only 20 g |
| Water rating | 3 ATM |
| Heart rate sensor | Chest strap, heart rate and HRV |
| External sensors | ANT+, Bluetooth (3 connections) |
| App | Garmin Connect |