All phones slow down over time. As hardware gets older and software gets newer, it’s inevitable. But there’s another reason your iPhone might be slow: the battery.

This phenomenon was first proposed in a Reddit thread, and then subsequently in a blog post by John Poole at Geekbench. Now, Apple has confirmed that it slows down iPhones with aging batteries. Here’s why it happens, and what you can do about it.

Apple Throttles Performance as Battery Health Decreases

RELATED: Debunking Battery Life Myths for Mobile Phones, Tablets, and Laptops

As your battery gets older, its health degrades. Over time, the battery is able to hold less and less of a charge—so a battery that lasted 12 hours when it was new might only last 8 after a few years under the same conditions. This is normal, and it happens on every device you own with a lithium-ion battery: phones, laptops, tablets, and even other gadgets like smart watches.

There are some things you can do to prolong a battery’s health (like avoiding full discharges, and keeping it away from heat and cold), but it happens to every battery eventually.

The problem, Apple discovered, is that the last few generations of iPhone experienced crashes when this happened. Instead of just having lower battery life, the phone would also shut down unexpectedly whenever the phone tried to pull more juice than the battery could supply.

Their “fix” was to slow down your phone’s processor once the battery health degrades to a certain point. In a statement to TechCrunch, Apple said:

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.

In other words: once your phone’s battery is shot, your processor will slow down, too. This is by design.

How to See If Your Phone Is Affected

To see if your phone is affected by this phenomenon, you can download a 99 cent app for your phone called Geekbench. Start the app, choose the “CPU” option, and then tap the “Run Benchmark” link.


You’ll get a results screen like this:

This iPhone 6 has definitely been throttled as a result of its battery.

Here are the ideal single-core scores for the affected phones:

  • iPhone 6 and 6 Plus: 1620
  • iPhone 6s, 6s Plus, and SE: 2500
  • iPhone 7: 3500

If your score is significantly lower than that—as in, hundreds of points lower—then your phone is probably throttling its CPU due to battery health. This is very likely if your phone is more than two years old or so. (Note: It’s unclear if the “Plus” models are affected by this, as Apple’s statement is vague, but running the CPU benchmark should let you know. Models earlier than the iPhone 6 should not be affected.)

Replacing the Battery Will Give Your Phone New Life (in More Ways Than One)

If your phone is indeed slowing down as a result of poor battery health, replacing the battery will give your phone new life. Not only will you get a longer-lasting battery by replacing an old one, but your phone should jump back up to its top speed. It won’t necessarily be as fast as the day you got it (remember, new software will still slow it down eventually), but it should last you a bit longer.

Replacing your battery is easy: just take it to the Apple Store and ask them. It costs you $80 for a replacement (unless you have AppleCare+, in which case it’s free as long as your battery is below 80% of its original capacity). You could have it done for less from a smaller third-party shop (or by doing it yourself), but we recommend going with Apple for best results—they won’t cover any mistakes you or your neighborhood shop make.

“But $80? Screw that!” I can already hear some of you say. Hear me out: if the alternative is buying a new phone, $80 is not a bad price.

Think of it this way: you paid $650 (at least) for that phone when it was new. If it lasts three years before battery life and performance suffer to the point of being frustrating, that means you paid about $215 per year of solid iPhone usage. A battery replacement won’t make that phone last forever, but even if it extends that phone’s usability by one year, $80 isn’t a bad price to pay.

Now, there’s a lot more we could say on the subject—is Apple doing a bad thing here?—but it’d be mostly speculation. Lots of people are claiming this is “planned obsolescence” in action (if your phone is slow, most people assume they need to buy a new phone—not replace the battery). But Apple argues that this is necessary to keep the phone working past a certain point, since without the CPU throttling, phones would start shutting down randomly after a couple years. We’re skeptical of Apple’s reasoning, but we can say one thing for certain: Apple’s communication was horrible on this issue, and they deserve criticism for how they kept their users in the dark for almost an entire year.

Whether you give Apple the benefit of the doubt or not, though, this is the reality iPhone users are stuck with for now. So if your phone is a few years old and is feeling a little slow, a new battery can go a long way—even if it is $80.

Image credit: Bloomicon/, Poravute Siriphiroon/

Profile Photo for Whitson Gordon Whitson Gordon
Whitson Gordon is How-To Geek's former Editor in Chief and was Lifehacker's Editor in Chief before that. He has written for The New York Times, Popular Science, Wired, iFixit, The Daily Beast, PCMag, Macworld, IGN, Medium's OneZero, The Inventory, and Engadget.
Read Full Bio »