Earlier quoted context omitted.
FWIW my iPhone 7+ went 5 years and holds a charge for ~12 hours. It was just at 78% when I replaced it a few weeks ago but TBH that number is very... random (I used to do phone repair). If you have a charger at your desk/car then honestly you could likely go even longer. I've seen people struggling after 2 years though so it's rather random. Just a random N=1 sample for you
12 hours is laughably small running time
That was with a few hours of screen time - I found that it didn't matter to me because I'd just plug it in at home/work. I'd call it "servicable" but certainly not great - but for 5 years I was personally surprised.