I don’t trust the capacity estimates. I sold my 8 plus after 10 months and it still showed 100%. Unless my battery came with 105% capacity, that’s hard to believe.
My wife’s launch x finally dropped to 99% a few months ago. It’s at 97% now. She’s a very heavy user and even uses a battery case which adds heat and stress to the internal battery.
My 2 month old 8 plus and my daughters 8 plus both still show 100%.
As for proper charging habits, it’s true that batteries hate heat and extremes. Going from 40-80 and always keeping it cool will extend their life. I used to be a battery ocd fool with my phones. At the end of the day it’s NOT worth it! This isn’t an electric car battery that costs thousands of dollars. If you keep your phone for 2 years and the capacity has dropped, spend the $80 for a new battery or buy a new phone. Making extremely impractical and annoying life changes to babysit a battery isn’t worth it when the payoff is saving $80 over 18-24 months. You can beat the hell out of your phone and not notice any capacity loss that will affect your usage for at least a year. If you want to save $80 and constantly monitor your battery then go ahead. I used to charge to 80% and never overnight. It feels much better to just charge to 100% and forget it.