Why 100% battery is so necessary? Poster just below you said he traded in his old phone and it was showing 100% battery life.
Are you draining your phones to 0% often? Maybe that's why your batteries wear prematurely.
I bought used Pixel 6 phone...
Don't do it. Just buy used. For price of your "plan" you can have 10x more phones over the same time period.
Yes, that's why a wise person don't buy new shiny phone every year.
Pixel 5 here. Bought it in mid-2022 on Swappa. Have since replaced the battery with the iFixit kit, and installed a new screen after a bad drop. I'm on LineageOS 22.2 (Android 15) and haven't bothered to update it to LOS 16. I do plan to try...