I had the Apple Watch track me during my hour long bike tours, GPS and heart rate sensor on and all, without any problems and with battery left to spare at the end of the day.
Seven to eight hours is probably the critical mark, but anything below that is no problem at all.
Ultramarathons (full 100 miles) usually takes between 24-30 hours according to one source (WaPo). I'm guessing you're thinking of regular 26.2 mile marathons.
To be wildly pedantic, an ultramarathon is anything over 42.2km (26.2mi). It's perfectly possible to do an ultra with an Apple Watch if you're only going 50km (even I can manage 50km within the 8h battery life.)
Yeah, ok, no you can’t do that with an Apple Watch. Seems an alright trade-off for Apple to make. The amount of people running ultra-marathons is probably miniscule.
I had the Apple Watch track me during my hour long bike tours, GPS and heart rate sensor on and all, without any problems and with battery left to spare at the end of the day.
Seven to eight hours is probably the critical mark, but anything below that is no problem at all.