Apple has confirmed it slows down old iPhones.

Technically, the company admitted it slows down processors used in iPhone 6, iPhone 6S, iPhone 7, and iPhone SE. These have aging lithium-ion batteries that might cause random shutdowns. So, to prevent your older iPhone from shutting down, Apple pushes out an iOS update that throttles the phone’s CPU. Slower performance is a side effect, unfortunately, and that could force you to upgrade to a newer iPhone.

If you can't afford the latest and greatest iPhone, or maybe you just want your expensive iPhone to perform well for more than a year or two, there is a workaround: Replace the phone's battery. Here's how to tell if it should be switched and what your options are if that's the case.

Should your iPhone battery be replaced?

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To determine whether your iPhone's battery should be replaced, open the Settings app, then tap Battery, and look for a notice at the top that will say something along the lines of: "Your iPhone battery may need to be serviced." If you see that, your battery likely needs to be switched. Keep in mind Apple's CPU-throttling update only affects iPhone 6, iPhone 6S, iPhone 7, and iPhone SE models.

Note: Your iPhone needs to be running iOS 10.2.1 or later to see the notice.

How to replace your iPhone battery

You have three main options:

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Apple

If you want Apple to replace your iPhone's battery, take your iPhone to an Authorized Service Provider or Apple Retail Store. You can also contact Apple Support. Apple’s one-year warranty, AppleCare+, includes service overage for a defective battery. In other words, if you have AppleCare+ and Apple determines the battery is defective, or if your iPhone is still under warranty, the replacement will be free.

You can check the status of your coverage here. If your iPhone isn't under warranty and doesn't have service coverage, Apple offers a battery replacement program for $79 (£79 in the UK). Apple will put a temporary authorisation on your card to cover the maximum repair fee. This covers any additional damage it might find, but if your iPhone has no other damage, Apple will only charge the battery fee.

Update: Apple recently announced that anyone with an iPhone 6 or later can get a battery replacement for $29 - even if the phone is out of warranty. This new fee will go into effect starting in late January 2018 through to December 2018. That's a $50 savings. 

Apple is also offering to replace some iPhone 6S batteries for free for people who bought an iPhone 6S manufactured between September and October 2015 and are experiencing random shutdowns. You can check your serial number to see if you’re eligible here. Either way, if you ship your iPhone to Apple, the entire battery replacement service may take a while, as Apple needs to collect your phone and fix it.

If you take it to a store, the repair can usually be done in one visit, or, in more difficult cases, up to three to five days, Apple said.

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Third-party repairer

If your AppleCare+ warranty is expired, or if your iPhone is out of warranty, or if you aren't comfortable performing a DIY battery replacement, you can pay a third-party repair company to do the swap for you. You can either go through a local one or an online one. The key is to research them well, do price comparisons, and ask about the quality of their parts, warranties available, and repair times.

Depending on where you're located, here are some suggestions:

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Do it yourself

This is no easy task. The process involves unscrewing the back of the phone, then removing two metal plates, and heating up the phone with the lid back on so that the glue comes off the battery. You then have to do all that again, in reverse, to put the new battery in. You’ll need smartphone repair tools, which cost around $30, or an iPhone battery replacement kit, which also cost around $30.

We recommend using the iFixit guides below (iFixit also sells its own $29 battery replacement kit), which have clear instructions, as well as YouTube tutorials like this one and this one.