I ran a marathon with the Apple Watch Ultra 2 against Garmin Fenix 8

The Garmin Fenix 8 and Apple Watch Ultra 2 are two of the best sports watches and two of my favorite devices, both of whom have worn for long distances, in particular to follow my marathon training.

I ran the London Marathon 2025 and wore both watches 2:26:48. Both impressed me in particular for the GPS accuracy and helped me to cross the race in the first half – the fact that I went out too quickly and was slower was certainly my fault, not the watches!

Both watches are at the more expensive end of the sports watch spectrum, but the Apple Watch Ultra 2 is cheaper at 799 US dollars compared to 999 US dollars for the cheapest Fenix 8 model -The 47 -MM -SAPHIRE I was wearing retail at 1,099.

In view of the price and the impressive specifications at both watches, you can expect a high level of performance. How did you perform at the London Marathon?

GPS accuracy

(Credit: Future)

The official marathon distance is 42.195 km, but you usually have to continue to run than this distance in the race itself, while dodging people and going around the corners than the measured route.

Nevertheless, I was able to capture (mostly) on the blue lines on the street, which marks the fastest route around London on the race day, and the total removal of the Apple Watch of 42.26 km is impressive near the official distance.

The Garmin Fenix 8 measured 42.47 km, which is still very good, and the GPS traces of both watches are almost identical.

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London Marathon GPS Track — (Photo credit: DC Rainmaker Analyzer)

Apart from Canary Wharf, where watches tend to go wrong in the London marathon. Both watches were still pretty good here, but the Garmin had a somewhat more precise GPS route.

Overall, I was able to cross the race with one of the two watches and the LAP warnings were closely aligned with the markers on the course. This was the high level of accuracy that they offered thanks to the dual band GPS available on both available dual band.

Winner: Apple Watch Ultra 2

HR accuracy

Garmin Fenix 8 and Apple Watch Ultra 2 hours

(Credit: Future)

I have not worn a heart belt frequency monitor in the race, which I usually do during training for the most accurate heart rate. But I wore in earlier marathons chest straps and know how my heart diagram should look rough in a long race.

I would expect a steady increase during the race because the effort is becoming increasingly difficult, and that was exactly what the Fenix 8 rose on this day and rose strongly to my maximum heart rate when I tried to sprint the house straight.

London Marathon HR Graph

(Photo credit: DC Rainmaker Analyzer)

In contrast, the Apple Watch Ultra 2 tried to my heart rate in the first half of the race, usually no data and read when it was the case.

After about an hour, however, it started to read the heart rate correctly, and mostly fit the Garmin for the rest of the race.

Winner: Garmin Fenix 8

Battery life

Garmin Fenix 8 and Apple Watch Ultra 2

(Credit: Future)

I calculated both watches overnight, so they were 100%at the beginning of the day. I always had it activated on the screen and both used both in the most accurate and intensive GPS mode to follow the run.

On Sunday at 6 p.m. the Garmin Fenix 8 was 84% and the Apple Watch Ultra 2 at 67%, so the Garmin wins the day during the battery life.

I would expect to use the Fenix 8 for another week without charging, partly because I will be much less active than usual if I recover after the marathon.

The Apple Watch Ultra 2 would still last for two days, including a marathon, which is impressive for a smartwatch with such a large and bright screen. However, the battery life is still an area in which sports watches like the Fenix 8 have the edge.

Winner: Garmin Fenix 8

Verdict

Apart from the dodgy first hour of Apple Watch Ultra 2 from the very beginning of the heart rate tracking, I would say that both watches did an excellent job at the London Marathon, and their GPS accuracy impressed me particularly on a tricky course.

The Garmin Fenix 8 is my main sports clock and remains, partly because of its battery life. But I also enjoy the abundance of analyzes that she offers during training for a marathon.

Com Come Race Day itself, but I would be happy to rely on one of these watches to help me do the course.

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I ran a marathon with the Apple Watch Ultra 2 against Garmin Fenix 8 – here is the winner

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