Facing criticism after last week's statement on CPU management, Apple has released an open letter about iPhone batteries on its website. Not only does the letter address technical aspects of battery performance, but it offers an apology and clarification of the issues.
Quite possibly the best news for iPhone owners is a reduction in the fee required to replace an iPhone battery. Those with an iPhone 6 or later and a battery needing replacement can get the job done for $29. This represents $50 in savings over the previous cost of $79. Apple will offer the reduced battery replacement fee starting in late January through December 2018. iPhone users can check for a battery service message under Settings -> Battery.
Offering $29 battery replacement service for out-of-warranty iPhones is just step one of Apple's changes surrounding the issue. In early 2018, iOS will receive further updates showing more detailed information about the health of the iPhone battery. This change is intended to help iPhone owners better understand how the condition of the battery might be affecting performance on their device.
Details on the way iOS manages power can be found on Apple's iPhone Battery and Performance page. In a nutshell, when batteries chemically age they are less effective at delivering power. Since January, iOS has added performance management features to prevent spikes of power demand when batteries are old. In some circumstances, this means reducing the maximum performance of iPhone components such as the CPU to prevent devices from shutting down.