Around 20% apparently do: https://c9ac71a8282e1fecd95e-f07dbcddcacf0d4c572ea7178ee6902...

From: https://www.sellcell.com/blog/how-often-do-people-upgrade-th...

It's not common (I think average upgrade cycle on iPhone is a little more than 3 1/2 years now, and getting longer every cycle) but it's not unheard of. The iPhone hold value well enough that you can often trade it in at something like a $200 discount and just get the new one.

Considering the cost of a battery replacement, it's not the worst value proposition in the world.

I do for my iPhone yes. It's definitely overkill and certainly not recommended for 99% of people.