Have you noticed that your iPhone has gotten a little slower lately? Well, you’re not the only one. Recently, a whole lot of iPhone 6 and 7 owners noticed performance hits after updating the operating system.

Apple (along with lots of other phone makers) has long been accused of slowing older phones down via iOS updates as a sly way to get you to upgrade to their newer, faster phone. But those rumors have remained, well, mostly unsubstantiated rumors and accusations.

Here’s what makes this latest case a little different. iPhone owners on Reddit noticed that their performance woes seemed to disappear when they replaced the battery. These findings were supported by a Geekbench analysis indicating that a recent Apple update—designed to prevent random shutdowns—quietly throttled the CPU in iPhone 6, 6s and 7 units, probably as a way to support aging batteries.

To see if we could confirm the findings, we rounded up some 2- to 3-year-old iPhones equipped with factory original batteries and iOS 11 for an informal test. We expected to see some difference, but the results frankly blew us away. We took four iPhones that consistently benchmarked as low as 40% of Primate Labs’ published performance averages, gave them a battery transplant, and re-ran the benchmarks. And ran them again. And then ran them some more. The result? They not only got that missing 60% back, but they beat the Geekbench aggregate scores in every single test we ran. Some phones saw a consistent performance boost of over 100%—not just in benchmarks of course, but also in the snappiness of their response during day-to-day use.

Battery benchmark findings.

What’s more, today Apple itself weighed in on the controversy and confirmed that their software update does, indeed, impact performance. But, the company told The Verge, the performance slowdown was designed to support aging devices.

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.

Reasonable enough. Batteries wear out—it’s a fact of life. And one way or another, performance degrades along with it. Apple has historically claimed that the iPhone battery is designed for a 400-500 cycle life (their somewhat hidden battery page now claims 500, but has changed over the years). Every full charge and discharge is a cycle. If you use your battery up every day, that’s 500 days. Most of us go a bit easier on our batteries, and in general, we recommend replacing your battery every 18 to 24 months.

When your battery is wearing out, you’ll see degraded battery life. Your phone may shut off unexpectedly before it reaches 0%—perhaps when you open the camera app or browse an intensive web page. Apple’s software update makes this a bit less painful, deliberately reducing the maximum current that the phone draws by throttling performance.

This is a reasonable change. Being mad at Apple for pushing a software update that goes gentler on old batteries is, frankly, a little dumb. Of course they should help make your phone last as long as possible.

But there are some things that you should be mad at Apple for doing. They don’t disclose anywhere on the iPhone that the battery life is limited. They’re limiting performance silently, without telling you that the battery is the culprit. They’ve purged the App Store of any app that can tell you the cycle count on your battery. (Although you can still find out by plugging your phone into your Mac and using CoconutBattery.) They don’t sell parts to anyone, even neighborhood repair shops. (Not that we’re complaining—we’ll happily sell them to you!) And they oppose Right to Repair legislation that would guarantee consumers access to repair parts.

So what’s the bottom line? Plan on changing your battery regularly, just like you change the oil in your car. You can do it yourself. It’s not hard. Millions of people have used our guides. For your convenience, here are some instructions.

For the love of all that is holy, don’t replace your phone because the battery is worn out! Take a deep breath, get out your screwdriver, and make your phone fast again.

Jeff is a teardown engineer with iFixit.

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