In a letter to Senator John Thune, Apple confirmed that it would bring transparency to the way its iPhones handle CPU slowdowns due to aging lithium-ion batteries. If you have an Apple Developer account, you can check out the solution the company has baked right into its upcoming iOS 11.3 release. As first noticed by 9to5Mac, the iOS 11.3 beta has a new "Battery Health" system preference screen, with a "Performance Management" section.
In the new "Peak Performance Capability" section of the Battery Health screen, you can now see the maximum capacity of your battery (as compared to when it was new), and you can also see if the operating system has applied a performance management tweak due to an "unexpected shutdown because the battery was unable to deliver the necessary peak power," as the explanation reads.
Image Credit: 9to5Mac
9to5Mac notes that all devices that upgrade to the new iOS will start with this management system disabled. Your iPhone will enable it if it shuts down unexpectedly, and you can disable it in the Battery Health section now. In its letter to the senator this past weekend, Apple said that newer iPhones like the 8, 8 Plus and X use a more advanced system to manage battery performance.