Battery health concern on iPhone 15

As the iPhone 15 battery has empirically shown to stay above 80% for 1000 cycles it would lose 1% for ever 50 cycles. 320/50=6.4, 100-6.4=93.6 after 320 cycles the expected value would be 93% (as the gauge truncates, not rounds). So it is a little below where it is expected to be, but, as batteries are nasty chemical analog devices rather than nice digital devices, the gauge won’t always be linear. So don’t worry about it.

The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates. Here's more information→About Optimized Battery Charging on your iPhone - Apple Support

Even rechargeable batteries get worn down and 1-2% health loss per month is perfectly normal. Referring to the "Your battery's maximum capacity" section of the support article: iPhone battery and performance - Apple Support - "A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions." Apple apparently only considers it unusual (and covered by warranty) if a battery drops below 80% maximum capacity in less than a year after you receive it. Ergo, some storage loss as you use it is anticipated and acceptable. A possible 20% drop over the first 12 months equates to 1-2% drop per month being within the range of what Apple finds acceptable. "The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge." In other words, if maximum capacity is below 80%, the battery is below normal performance and worth replacing. A notification will appear about this. You can still use a device with a lower health percentage than 80% but for optimal usage you may wish to consider having it changed when it reaches 80% battery health.

What this basically means:

- If battery health drops a few percentage per month that is normal.

- If battery health drops below 80% before the end of the first year, contact Apple about a warranty replacement. (Apple will test it to determine its actual eligibility.)

- If battery health drops below 80% (you will see a warning message) after the first year, consider getting the battery replaced but anticipate paying for it.

From the document that you linked in your reply above........iPhone battery and performance - Apple Support

Batteries of iPhone 14 models and earlier are designed to retain 80 percent of their original capacity at 500 complete charge cycles under ideal conditions.

Batteries of iPhone 15 models are designed to retain 80 percent of their original capacity at 1000 complete charge cycles under ideal conditions.* With all models, the exact capacity percentage depends on how the devices are regularly used and charged.

Apple will not replace the battery unless it is down to 80% Battery Health.....even if you are willing to pay.

On average, it is normal to expect Battery Health to decline at 1% for every 40-50 charge cycles. Apple mentions that 50 charge cycles would be under "ideal" conditions, but it is unclear on what that might really be.

So, after 320 cycles, you could expect that the battery has declined 6-8%, so the battery would normally be at about 92-94% at this time.

Your battery is declining a bit faster than normal.

Replace the battery when it is down to 80%.

iPhone 15 and 16 are rated for 1,000 cycles.