I wish it was as easy as just buy $50 battery. But with a waterproof phone I don’t think waterproofing will be ip68 when I replace the battery and being able to just dunk my phone in water or run it under the sink when it’s Dirty is so freaking easy. I do find it kinda weird that you doing 80-20 made the battery worse I think it might be just newer battery tech/software but you saying that your new phone also has the battery degrade faster than your previous phone makes me wonder if maybe manufacturers are already doing 80-20 in the software maybe and mapping 80 to 100 and 20 to 0. And that charging it more often is worse than just doing 100% and charging it less. I think I am definitely going to need to setup some experiment to figure it out. And maybe going to ask honor for advice. Thank you for sharing this information.
https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries has a table explaining exactly what I wanted to know 10% discharge depth results in a larger total charge the battery can carry throughout its live than a 80% for example