All in all, I was extremely satisfied with battery life performance from the Apple Watch Series 5, especially with the always-on display activated. As always, your mileage may vary — and for the better if you finish the race faster! More here.
I don’t recognise these results at all. When my wife ran a marathon last year the following happened (full article is here)-
She had disabled the always on screen beforehand and only enabled the features she needed, but still it died less than half way through the marathon. If she had run a new world record of under 2:15:25 the Apple Watch would still have only just survived by 15 minutes.
This meant that we had no idea where she was and could not make sure that she was OK. She had lost her music and so had to run in silence and the Apple Watch did not record her completing the marathon- she only wanted to complete one marathon in her life, but the Apple records will not show it. Finally, we then had to wait for some time in the hope that she could complete the marathon and the worry was immense for all of the family waiting.