Third party apps use the ioreg parameter for battery condition. This can fluctuate up and down which is why Apple uses a different algorthm, which does not. Apple will not replace unless the Apple parameter is under 80%.I’ll share my experience with you in this regard. I had an iPhone 14 PM, and the battery quickly dropped to 83%, in just 15 months. Then it “magically” stopped at 83% 🧐
Other 6 months and the battery remained at 83%… which is technically impossible. My AppleCare+ was expiring in one month, so I called Apple customers support. The answer: at 83% we won‘t replace your battery for free. I opted for a trade-in for a new iPhone 16 PM, but just for your information I checked the battery with Battery Stats and the reported health was 78%, even if iOS insisted on 83%…
See my ioreg data fluctuation in this post.
I think the AppleCare+ expiration date is somehow “included” in the battery health algorithm … 😏
I think you’re right about this…my wife’s iPhone 13 Pro with AppleCare has been on 80% for six months!