Nick Harris-Fry

Fri, October 3, 2025

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I usually wear a dedicated sports watch, where battery life is measured in days or weeks, so the news that the Apple Watch Ultra 3 had six more hours of battery life didn’t initially sound that impressive to me.

However, I’ve used the Apple Watch Ultra 2 to run marathons before, and I know that Apple tends to be conservative in its battery estimates, so I was keen to see if the Apple Watch Ultra 3 could surpass the 42 hours it’s listed as lasting.

I had a trip to Inverness in Scotland lined up to run the Loch Ness Marathon, so I charged the Ultra 3 to 100% at 1pm on Friday afternoon to see how far through the weekend it could last.

The results were surprising, impressive and actually gave me a real shock. The watch didn’t run out of juice until Monday afternoon, just before I arrived home from the trip, and I had no fear of it dying during the marathon on Sunday morning.

Loch Mess Marathon battery test

Credit: Future

I used the Apple Watch Ultra 3 normally throughout the weekend, with the screen always-on and for sleep tracking on Friday and Sunday night.

I did take it off for the night before the marathon because I don’t look at any sleep tracking info on the morning of a race, so it saved some battery then by automatically going into low-power mode overnight.

Along with the marathon itself I also used the watch to track my shake-out run on the Saturday, and I used normal tracking settings for those runs, not the low-power GPS. I didn’t listen to music using the watch on the runs though, which can be a big battery drain.

Credit: Future

On the morning of the race — 44 hours after I charged it — the watch still had 51% battery, meaning I was confident it would last the event without a top up.

I finished the race in 2:24, and when I checked the battery shortly afterwards the Apple Watch Ultra 3 still had 27% left.

Naturally, a longer marathon time will drain more battery life, but there was enough juice left for a few more hours of running when I finished.

When I woke up the next morning, the battery life was in the red, but it still lasted the flight home. I put it into low-power mode when it hit 2% and that got me another hour or so — you could definitely extend the life longer with some strategic low-power stints.

How does it compare to sports watches?

Credit: Future

While three days of battery life including a marathon was impressive for the Apple Watch Ultra 3, you certainly can get more from the best sports watches.

I had the Garmin Fenix 8 Pro on my other wrist and it was still at 33% when I got home on Monday, having charged it to 100% at the same time as the Ultra 3. I also used the Fenix 8 Pro’s power-intensive LiveTrack feature during the marathon, which was sending my location to my family using its built-in LTE throughout.

Even smaller watches than the Fenix 8 Pro, like the Garmin Forerunner 970, will comfortably outlast the Ultra 3, but the Ultra 3 is a true smartwatch that’s more useful day-to-day — it showed my boarding passes for the flights to Inverness, as one example.

The Ultra 3 also charges incredibly quickly, and given that it now lasts over two days comfortably even with heavy use, you’re always likely to find a 30 minute window to charge it in that time.