One tangential weird experience: My iPhone 6s plus battery went obviously bad, as in reduced battery life and really big jumps down from 100 -> 70 and then from 40 -> 10 from minimal use. After months of dealing with the bad battery, hooking it up to my mac & running Coconut battery showed it was 46% good.

So I took it to the store for an official replacement (I decided I would pay for it). The genius ran a diagnostic which showed the battery as fine (green, he called it) and almost immediately started to tell me why it may be something else in the phone and started pointing me towards buying another phone instead of getting the battery replaced.

But for some reason their diag tool is worse than coconut battery or just wrong? If my battery were 60-70% good and they had lowered thresholds that's one thing, but my battery was long gone and they told me it's fine. And of course I insisted and the phone is fine now with a new battery.

I know there's probably a decent explanation for it but it certainly felt like they really wanted me to buy a new phone, and that their diag tool perhaps isn't the most truthful right now when it comes to battery health.