I bought this secondhand iPhone 11 last November 4, and 2023.
The iPhone 11 was discontinued in September 2022, so your phone is at least a year old and probably much older than that. It might be as old as 4+ years at this point.
When I initially got it, it was at 99% battery health
But, that may not have been the true reading because this appears to be one of those "too good to be true" things. No way to know really.
Today is December 23, 2023, and it’s at 89% battery health.
The battery is clearly defective if you lost 10% in the last 2 months. But, I still question whether it really was at a true 99% when you got it.
You know that the last iPhone 11 was shipped out in Sept 2022, so the battery is more than a year old. Battery Health normally declines at about 1% a month on average, so if he phone was at 100% a little more than a year ago, it would now be expected to be at about 88-90% Battery Health.
If the phone is really 2 years old, you would expect Battery Health to be closer to 80%
When the Battery Health is down to 80%, you need to have the battery replaced at the Apple Store or an authorized Apple Service shop.
