Tapping 'Battery Health' in the Battery Settings menu now brings you to a screen that displays your battery's maximum capacity and lets you know if your device is currently supporting normal peak performance.
Maximum capacity is a measure of battery capacity relative to when it was new. "Lower capacity may result in fewer hours of usage between charges".
Here's how Apple describes the new settings in the Battery Health section:
Your battery's maximum capacity
The Battery Health screen includes information on maximum battery capacity and peak performance capability.
Maximum battery capacity measures the device battery capacity relative to when it was new. Batteries will start at 100% when first activated and will have lower capacity as the battery chemically ages which may result in fewer hours of usage between charges.
A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge. Learn more about charge cycles.
As your battery health degrades, so can its ability to deliver peak performance. The Battery Health screen includes a section for Peak Performance Capability where the following messages may appear.
Performance is normal
When the battery condition can support normal peak performance and does not have the performance management features applied, you'll see this message:
Your battery is currently supporting normal peak performance.
Performance management applied
When the performance management features have been applied, you'll see this message:
This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. Performance management has been applied to help prevent this from happening again. Disable…
Note that if you disable performance management, you can’t turn it back on. It will be turned on again automatically if an unexpected shutdown occurs. The option to disable will also be available.
Battery health unknown
If iOS is unable to determine the device battery health, you'll see this message:
This iPhone is unable to determine battery health. An Apple Authorized Service Provider can service the battery. More about service options…
This may be due to having an improperly installed battery or an unknown battery part.
Performance management turned off
If you disable the applied performance management feature, you'll see this message:
This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. You have manually disabled performance management protections.
If the device experiences another unexpected shutdown, the performance management features will be re-applied. The option to disable will also be available.
Battery health degraded
If battery health has degraded significantly, the below message will also appear:
Your battery’s health is significantly degraded. An Apple Authorized Service Provider can replace the battery to restore full performance and capacity. More about service options…
This message does not indicate a safety issue. Your battery can still be used. However, you may be experiencing more noticeable battery and performance issues. A new replacement battery will improve your experience.