I ran a marathon with the Garmin Fenix 8 vs. Garmin Forerunner 965 — here’s the winner

The Garmin Fenix 8 and Garmin Forerunner 965 are both among the best sports watches you can buy, and I’ve used each one to track a variety of races in the past. But I wanted to put them head-to-head over the course of a marathon to see if any major differences arose.

I used both watches at the Seville Marathon on February 23, where I clocked a new PR of 2:25:32 aided by the GPS accuracy of the Garmin watches, which helped me to pace my race.

To compare the accuracy of the watches on the day, I kept an eye on the distance recorded when passing markers and checked the GPS trace from each after the race using DC Rainmaker’s Analyzer tool. I also compared the heart rate recordings from the two watches and how much the battery drained on each during the run. Here are the results.

GPS accuracy

The Seville Marathon has a flat and open course that winds around the city center. I’d say it has fewer sections that are under tall buildings than most city marathons, which makes GPS easier for watches, and both Garmins delivered highly accurate results for me on the day.

Both recorded similar distances that were close to the official marathon distance of 42.195km, and both produced very similar GPS tracks, even on tricky sections like a tight loop we ran around a cheer zone in a park in the center of the city.

I recorded 5K splits manually on the Fenix 8 and all of them bar one were within 50m of 5K as measured by the official markers on the course (one was 5.13km). Both watches helped me to stay on track and adjust my pace as I looked to get faster in the second half of the marathon.

HR accuracy

I didn’t wear a chest strap heart rate tracker during the Seville Marathon but I have done so in the past for marathons. With 14 marathons now under my belt I know what my HR usually looks like during the events.

Both watches produced exactly the kind of HR progression I’d expect to see in a marathon, with it rising gradually to reach close to my max in the latter stages of the race. The two watches were very similar throughout the race and although the Forerunner 965 seemed to have a few more erroneous dips, I’d say both did a great job on accuracy.

Battery life

I had both watches set to track GPS in the most accurate and power-intensive multi-band GPS mode, with the screens always-on. According to the DC Rainmaker Analyzer, the Fenix 8 battery burned at a rate of 3.86% per hour during the race, compared to 4.24% per hour on the Forerunner 965.

The Fenix 8 47mm I used is listed as having longer battery life than the Forerunner 965. Based on this marathon, it would offer just shy of 26 hours of multi-band GPS, compared with 23.6 hours on the Forerunner 965.

You can extend this battery life considerably by opting for a slightly less accurate GPS mode, but given that I was trying to run a PR, I wanted to have the best data possible available on my wrist.

Verdict

Both watches delivered impressively accurate results during the Seville Marathon, and there is no clear winner, but the Fenix 8 seemed to have marginally better HR accuracy and longer battery life, so it has the edge.

The Fenix 8 is a lot more expensive than the Forerunner 965, though, which is mostly down to its design — it uses more metal on its case, has a newer HR sensor and is dive-proof to 40m. In terms of sports tracking, both watches deliver similar excellent results and would certainly be among my top picks for marathon runners.

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