Apple has added a Battery Health section to some iPhone models in iOS 11.3. The performance management feature was created in response to Apple's CPU throttling controversy. The new section in the Settings app allows users to view their maximum battery capacity and disable the performance management feature.
All rechargeable batteries, including iPhone batteries, become less effective as they age. Older batteries have a lower charging capacity which can limit the amount of usage time between charges, and it can cause unexpected device shutdowns. The "performance management" tool throttles your CPU when peak battery performance can't be obtained by your device.
You can disable this feature by navigating to Settings > Battery > Battery Health, but you will run the risk of unexpected shutdowns. The best solution is to take your device to an Apple retail location for a battery replacement. Apple has begin offering $29 battery replacement to all iPhone owners to deal with the throttling controversy.
You can view your battery capacity in the Battery Health section. Newer devices will ship with 100% capacity. The performance management feature will only be activated on devices that experience an unexpected shutdown due to low battery capacity. The performance management feature is only available the iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, iPhone 7 and iPhone 7 Plus running iOS 11.3 or later. All listed iPhone models will initially begin with the performance management feature disabled. The iPhone, iPhone 8 Plus and iPhone X include smarter hardware to deal with performance management and effects of throttling should be less noticeable when it is activated.A normal battery should retain "80% of its original capacity at 500 complete charge cycles when operating under normal conditions," according to Apple. Newer devices that are not performing as listed should be taken in for repairs. Apple's 1-year warranty on iOS devices does cover defective battery replacements.
Devices with significantly degraded battery health will receive this message in the Peak Performance Capacity section:
Newest iPhone FAQs
"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…"
In cases that require more extreme throttling users may experience longer app launch times, lower speaker volume, backlight dimming and more. You can see a list of possible effects and learn more about battery health by reading Apple's iPhone Battery and Performance support document.