Endurometry
The fēnix 8 is the endurance option in this group, and size matters more here than anywhere else: Garmin sells it in 43, 47 and 51 mm, and the 51 mm gets roughly twice the GPS runtime of the 43 mm. The figures below are the 47 mm AMOLED model.
There is also a solar variant with a Power Sapphire lens, rated up to 28 days in smartwatch mode with solar charging.
Battery life compared
| Mode | Forerunner 265 | Forerunner 965 | fēnix 8 This watch | Venu 3 |
|---|---|---|---|---|
| Smartwatch mode | 13 days | 23 days | 16 days always-on 7 days | 14 days always-on 5 days |
| Battery saver mode | — | — | 23 days | 26 days |
| GPS-only | 20 hours | 31 hours | 47 hours always-on 37 hours | 26 hours |
| SatIQ / AutoSelect | 16 hours | 22 hours | 38 hours always-on 30 hours | — |
| All systems + multi-band | 14 hours | 19 hours | 35 hours always-on 28 hours | — |
| GPS + music | 7 hours | 10.5 hours | 10 hours | 11 hours |
| Max battery GPS | — | 34 hours | 81 hours | — |
| Expedition GPS | — | — | 17 days | — |
Official Garmin figures, gesture-activated display unless noted. Real battery life depends on the features you have enabled — GPS mode, music, Pulse Ox and always-on display all cost hours.
“—” means Garmin does not publish that figure separately for this watch. We leave it blank rather than estimate.
Specs
| Size | 47 mm AMOLED |
| Display | 1.4″ AMOLED |
| Storage | 32 GB |
| Positioning | GPS / GLONASS / Galileo · SatIQ · 多频 · LED 手电 |
| Released | 2024 |
Is it the right watch for your running?
The endurance pick. 47 hours of GPS, 81 hours in max-battery GPS mode, and an expedition mode measured in days rather than hours. It is also the heaviest and most expensive watch here.
Buy it if your running includes long mountain days, ultras, or multi-day efforts where charging is not guaranteed. If your longest run is a road marathon, you are paying for battery you will never use.
Related Tools
Training Pace Calculator (VDOT Zones)
Get your VDOT from a recent race and see easy, marathon, threshold, interval and repetition pace zones plus heart-rate zones.
Race Time Predictor
Predict your finish time at any distance using the Riegel power law and the Daniels–Gilbert VO2max model.
Pace Chart Generator
Enter a goal finish time and get a pace chart in both min/km and min/mile, a speed-to-pace conversion table, your tempo pace and a printable wristband.
Frequently Asked Questions
How long does the fēnix 8 battery last in GPS mode?
Up to 47 hours in GPS-only mode for the 47 mm AMOLED model (37 hours with always-on display), according to Garmin.
Do the different fēnix 8 sizes have different battery life?
Yes, dramatically. Garmin lists 28 hours of GPS for the 43 mm, 47 hours for the 47 mm and 84 hours for the 51 mm AMOLED models.
How much does the solar version add?
The Power Sapphire solar variant is rated up to 28 days in smartwatch mode with solar charging, versus 16 days for the 47 mm AMOLED.
Related Tools
Running Pace Calculator
Enter distance and finish time to get your pace per km and mile, average speed and per-kilometre splits.
Running Pace Converter
Convert between min/km, min/mi, km/h and mph, and see the implied finish time for 5K, 10K, half marathon and marathon.
KPH to MPH Converter (km/h to mph)
Convert kph to mph instantly: mph = km/h × 0.621371, so 100 km/h = 62.14 mph. Free km/h to miles per hour chart for road and running speeds, plus mph to km/h.
Race Time Predictor
Predict your finish time at any distance using the Riegel power law and the Daniels–Gilbert VO2max model.
Training Pace Calculator (VDOT Zones)
Get your VDOT from a recent race and see easy, marathon, threshold, interval and repetition pace zones plus heart-rate zones.
Age Grading Calculator
Convert a finish time to an approximate open-class (20–29) equivalent using Endurometry age factors — not official WMA tables.
Want a new tool or fix?
Tell us which calculator, pace chart or fix would help — we build what runners ask for. Replies usually come back in 1–2 days.