Primate Labs founder John Poole (and the brains behind Geekbench) basically confirmed these initial findings with some deeper analysis of his own, concluding, "The problem is due, in part, to a change in iOS. The difference between 10.2.0 and 10.2.1 is too abrupt to be just a function of battery condition. I believe (as do others) that Apple introduced a change to limit performance when battery condition decreases past a certain point."
Rather than let this controversy fester, Apple has now responded. In a statement provided to The Verge, Apple writes:
Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices. Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components.
Last year we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions. We’ve now extended that feature to iPhone 7 with iOS 11.2, and plan to add support for other products in the future.
Not surprisingly, Apple's language actually confirms Poole's findings that these speed limits were put in place for the iPhone 6/iPhone 6s/iPhone SE with iOS 10.2.1 and with the iPhone 7 in iOS 11.2. However, Apple is flatly denying that its efforts are a move to "encourage" users to upgrade to a newer iPhone.
In fact, this is exactly the conclusion that Poole suggested could confuse iPhone owners. "While this state is created to mask a deficiency in battery power, users may believe that the slow down is due to CPU performance, instead of battery performance, which is triggering an Apple introduced CPU slow-down," said Poole earlier this week. "This fix will also cause users to think, 'my phone is slow so I should replace it' not, 'my phone is slow so I should replace its battery'”.
In the end, Apple's decision to throttle performance on iPhones to cope with degraded battery performance seems like a sound practice. However, why couldn't the company just acknowledge what was going on? A simple prompt could have been displayed to let customers know that their iPhone is not operating at full speed due to an aged battery. That would then at least give customers the opportunity to have their battery replaced to resolve the issue. But instead, Apple with its typically secretive behavior left users in the dark, which in reality is a disservice to its loyal customer base.