Mine started doing this exact thing that you're describing about a month ago and the battery was faulty.View attachment 2366436 View attachment 2366435
iPhone was constantly restarting for some reason for few hours.
Then it stabilized. There is no panic logs on diagnostic.
Then it seems that charging takes very long time as you can see, from 6:00PM-9:00PM, the phone was on charger, but only charging from 60%-88%.
Then in the morning, it took 3 hours only charging from 83%-91%.
Off the charger for few minutes, then as soon as open Camera app, the phone will restart, battery goes down to 10%. Restart again, back to 90%. However, when iPhone shows 90%, phone will restart as soon as Camera app launches.
Finally, put phone back to charger, now charging normally.
The battery health shows as 92%. Apple won’t replace battery health is above 80%. So if the battery is the issue, then what should I do?
iPhone battery health was less than 400 cycles and battery health above 92% (Might have been 94%, I don't remember exactly).
Third-party apps like Coconut Battery gave the same stats and no warnings about anything when I plugged my iPhone into the Mac and opened the app. Other apps rated the battery health as "great", "no significant wear", etc.
But it kept draining suddenly for no reason and either charged way too quickly or way too slowly. Sometimes when drained, it would shut down and not turn on unless I charged it with a 12 or 20 watt charger.
But I suddenly noticed the display bulging in one corner and immediately knew the battery was "pillowing".
I got it replaced and now it's fine again.
*Yes, all batteries are dying. But it's supposed to happen exponentially, over many months and years. It's not supposed to plummet drastically within a few days or weeks.