As previously promised, Apple released a new feature to help users check battery health and disable performance throttling in iOS 11.3 beta 2. If you have the iOS 11.3 beta 2 installed, you can find the feature under Settings, Battery, Battery Health. This view includes information about the maximum capacity of the battery in the device, and describes whether the battery has degraded to the point where it can no longer offer peak performance.
Currently, performance management may be enabled by the system on iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, iPhone 7 and iPhone 7 Plus. With iOS 11.3, it is now possible to disable performance management, stop the throttling, and restore full speed. Battery capacity can be viewed on any iPhone introduced in 2014 or later, starting with iPhone 6.
The Maximum Capacity readout gives an estimate of the amount of total capacity the battery can hold. New phones should report 100% capacity. A lower capacity means that the iPhone will not as long between charges. If the battery is still in good health to provide peak power, it simply confirms that the battery is supporting the maximum performance it can. If the iPhone unexpectedly shutdowns because it cannot sustain maximum performance, the device will enter this state with performance management enabled. Performance management slows down the CPU dynamically to reduce peak power demands on the battery.
If you do not want to be throttled, users can get a battery replacement as ever or disable the throttling (new in iOS 11.3). To disable, select the blue Disable link.
Note that if you disable performance management it cannot be toggled on again until the device unexpectedly shuts down. Apple says that it will automatically re-enable performance management each time the device unexpectedly shuts down.
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