As we know, under the premise of not telling the users, Apple secretly restricts the performance of the old iPhone, which is obviously not acceptable to you. Though Apple has apologized for the two times, and reduced the cost of replacing the new battery.
In the end, Apple chose to compromise its promise in the new iOS 11 version, allowing users to manually turn off iPhone CPU performance throttle, and this version is iOS 11.3.
As you can see in the latest Apple’s instructions, the iOS 11.3 official version has added the Battery Health, and you can see the Maximum Capacity and Peak Performance Capability two suboptions.
For maximum capacity, is the battery capacity, if the percentage of the lower the number, then the less natural life, and to a particularly bad time, you are prompted to replace the battery (after the 500 times full charge, Apple said the battery will drop to 80%).
The peak performance is what we say “turn off iPhone CPU performance throttle”, if your battery performance is OK, you are free to choose whether to turn off , and if the battery performance is not satisfactory, then you can manually turn off, but the system will advise you when turn off iPhone CPU performance throttle, your iPhone maybe restart or shutdown inexplicably.