Some recent iOS upgrades slow down the processing speeds of iPhones with degraded batteries.
The processor slowdown is (according to Apple) intended to prevent unexpected power-related shutdowns and other problems in older iPhones that have batteries whose performance has degraded over time, not to boost sales of just-released newer iPhone models.
A long-circulating piece of technology lore surrounding the release of new iPhone models holds that Apple unleashes furtive iOS updates in order to dramatically slow down existing iPhone models just before the release of newer models in a case of "planned obsolescence" intended to increase sales of the latest iPhones. An example of the rumor was illustrated in an episode of the Netflix series The Unbreakable Kimmy Schmidt:
On 21 September 2017, a blog post strongly implied that a Harvard study had proved the rumor true:
If you were Apple, what tricks would you utilize to increase the sales of your latest product?
If you know corporations, you’d know they use any possible trick they can as a generality to increase their profit: think of how huge a factor it would make in the sale of new iPhones if the old ones became slower.
People have made the anecdotal observation that their Apple products become much slower right before the release of a new model.
Now, a Harvard University study has done what any person with Google Trends could do, and pointed out that Google searches for “iPhone slow” spiked multiple times, just before the release of a new iPhone each time.
The blog, instead of linking to a peer-reviewed item published in an academic journal, cited a 29 July 2014 article published by a British tabloid. That source material similarly and repeatedly referenced a study:
A new study is backing up long held suspicions that Apple slows down older models of its iPhones to encourage users to buy a new release.
The U.S. study analysed worldwide searches for 'iPhone slow' and found that the search term spiked significantly around the time of new iPhone launch ... The study, compiled by Harvard University PhD student Laura Trucco, follows claims that the Cupertino-based company is deliberately sabotaging its old products.
Writing for the New York Times, Sendhil Mullainathan, a professor of economics at Harvard, described the results as 'striking'.
The referenced "study" was mentioned 26 July 2014 New York Times "Upshot" blog post authored by Harvard economics professor Sendhil Mullainathan, which he describes it as a graduate student's casual experiment using Google Trends:
Generally, my students know enough to ignore my grumbling. But in this instance, Laura Trucco, a Ph.D. student in economics at Harvard, followed a hunch. She wanted to see whether my experience was unique. But how? When people become frustrated with a slow phone, she reasoned, they search Google to figure out what to do about it. So, in theory, data on how often people search for “iPhone slow,” as provided by Google Trends, can measure the frustration globally. (Data for only the United States show similar results.)
In the Daily Mail, Mullainathan was quoted as having "described the results as 'striking.'" However, the context offers a completely different picture:
Yes, phones feel slower over time as they hold more software and as our expectations of speed increase. But the spikes show that the feeling doesn’t grow gradually; it comes on suddenly in the days after a new phone is released.
Yet that’s all it shows: People suddenly feel that their phone is slowing down. It doesn’t show that our iPhones actually became slower. Imagine that someone points out a buzzing sound in your office. Until then, you hadn’t noticed it. But now you can’t hear anything else. Perhaps this is the digital equivalent of that experience: Hearing about a new release makes you contemplate getting a new and faster phone. And you suddenly notice how slow your old phone is.
Mullainathan contrasted the Google Trends search with a similar one involving Android products, noting an absence of similar results and positing:
This data has an even more benign explanation. Every major iPhone release coincides with a major new operating system release. Though Apple would not comment on the matter, one could speculate — and many have — that a new operating system, optimized for new phones, would slow down older phones. This could also explain the Samsung-iPhone difference: Because only 18 percent of Android users have the latest operating systems on their phones, whereas 90 percent of iPhone users do, any slowdown from a new operating system would be naturally bigger for iPhones.
The important distinction is of intent. In the benign explanation, a slowdown of old phones is not a specific goal, but merely a side effect of optimizing the operating system for newer hardware. Data on search frequency would not allow us to infer intent. No matter how suggestive, this data alone doesn’t allow you to determine conclusively whether my phone is actually slower and, if so, why.
A December 2017 article from Geekbench charted that some older iPhones did seem to exhibit slower performance after particular iOS upgrades, but that their speed picked up once their batteries were replaced:
While we expect battery capacity to decrease as batteries age, we expect processor performance to stay the same. However, users with older iPhones with lower-than-expected Geekbench 4 scores have reported that replacing the battery increases their score (as well as the performance of the phone). What’s going on here? How many phones are experiencing decreased Geekbench 4 score?
At that juncture, Apple finally acknowledged that yes, some recent iOS upgrades did throttle processor speeds in some older model iPhones. But, according to Apple, that action was intended to address a problem with unexpected power-related shutdowns (and other issues) in older phones caused by their batteries' degrading over time and was not — as rumor commonly claimed — deliberately coincident with the release of newer iPhones in order to drive sales:
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.
Although, as Geekbench noted, the issue might nonetheless serve to increase sales of newer iPhones, whether or not that was Apple's intended purpose -- in the absence of any explanation for the sudden change in performance, many iPhone users may assume the performance problem is related to their phones (and not specifically to their batteries) and therefore opt to upgrade their iPhone models:
If the performance drop is due to [Apple's] "sudden shutdown" fix, users will experience reduced performance without notification. Users expect either full performance or reduced performance with a notification that their phone is in low-power mode. This fix creates a third, unexpected state [which was] created to mask a deficiency in battery power [but which] users may believe is due to CPU performance instead of battery performance. This fix [can] cause users to think “My phone is slow so I should replace it,” not “My phone is slow so I should replace its battery.” This will likely feed into the “planned obsolescence” narrative.
On 21 December 2017, a class action lawsuit was filed against Apple over the slowdown issue.