iPhone slowdown blamed on controversial fix for aging batteries

Older iPhones getting unexpectedly slower could be down aging batteries rather than iOS inefficiency, with Apple said to be artificially throttling handsets to prolong runtimes. For years, Apple – and other smartphone makers – have been accused of quietly encouraging so-called "planned obsolescence," where the experience of using a device is artificially worsened to encourage upgrades.

This latest batch of speculation taps into that controversy too, though there are arguably good reasons for why it might be happening. Discussion began after a Reddit user observed the iPhone 6s he was using with various iOS 11 updates was noticeably slower than an iPhone 6 Plus running the same software. That's despite the processor of the iPhone 6s being – on paper – faster.

A Geekbench test of processor performance seemed to bear out those anecdotal observations. With the original battery, which was showing a roughly 20-percent wear level, the phone scored considerably lower in Geekbench than after the battery was replaced. Results were unaffected whether or not iOS' low power mode was activated.

"From what I can tell, Apple slows down phones when their battery gets too low, so you can still have a full days charge," the Redditer concluded. "This also means your phone might be very slow for no discernible reason."

The discussion caught the attention of the Geekbench team itself, which set about exploring the issue. "While we expect battery capacity to decrease as batteries age, we expect processor performance to stay the same," Primate Labs founder John Poole explains. "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)."

Poole plotted the distribution of iPhone 6s and iPhone 7 benchmarking scores, observing that it does indeed appear to be the case that processor performance reduces as battery condition decreases. However, he also suggests that Apple's change in iOS 10.2.1 to address unexpected iPhone shutdowns has also artificially limited performance as battery wear passes a certain threshold. A similar change appears to have been added in iOS 11.2.0 for the iPhone 7, he claims.

As for why that might be the case, though some will be quick to accuse Apple of trying to nudge people into upgrading, there's a less nefarious option which makes a lot of sense. By throttling CPU performance it's more likely that the iPhone will last through a full day, even if it's slower at running apps during that time.

"If the performance drop is due to the "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. 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" John Poole, Geekbench

A phone that's functional when you need it is clearly better than one which runs out of battery quicker. Nonetheless, there are concerns that Apple isn't doing what it might to communicate the issue. The company has a battery replacement program, which charges $79 to switch out the old pack in an iPhone for a new one. However there's no obvious way to know if subpar performance you're experiencing is, indeed, down to this throttling, or something else.

It's par for the course that, over time, lithium-ion batteries will progressively hold less of a charge. That, after all, is the reason Apple offers out-of-warranty battery replacements. With the iPhone 6s now around two years old, battery degradation is unsurprising. All the same, how that is being translated to user-experience is something we still know little about.