Apple has slashed the cost of replacement batteries for some of its iPhone models after admitting software updates have slowed down some handsets with ageing batteries.

The tech firm has apologised to customers and says out-of-warranty replacement batteries for the iPhone 6 and newer models will now cost £25 rather than £79. Here's how to find out if you're affected and what to do if you are.

Why do some batteries need replacing?

Apple is facing lawsuits in the US over the slowing down of older iPhones.

Last week it released a statement admitting that some updates for iPhones – aimed at preventing devices from unexpectedly turning off – have caused some older models to take longer to launch apps and run more slowly.

Apple claims it initially thought this was due to a combination of a temporary slowdown caused by the upgrades and minor bugs in them that were later fixed. But it's now said it's also partly due to the "chemical ageing" of batteries in iPhone 6 and 6s models.

How do I know if my phone's affected?

The issue affects older iPhones. For now, you'll have to rely on your own experience – if you've noticed slower performance after a software update, or your handset's unexpectedly shut down with some battery remaining, it may be as a result of having an older battery.

Apple says it plans to issue an iOS software update which will include a new feature which lets you see if the condition of your battery is affecting your phone's performance. This update's expected in "early 2018".

How does the replacement scheme work?

We don't yet have full details of the scheme but here's what we know so far:

  • The price of out-of-warranty replacement batteries has been cut to £25. Apple initially said the price cut would be effective from late January, but it now says this applies "immediately".
  • The price reduction applies to iPhone 6 or newer models, but not to earlier models, such as the 5, 5s and 5c. (We've asked Apple to confirm if this also applies to the latest iPhone 8, 8 Plus and X models, which were released in September and November last year. We'll update this story when we hear back.) Other Apple devices such as iPads aren't covered by this scheme.
  • Batteries can be replaced at Apple stores or 'Apple-authorised service providers'. Apple hasn't officially confirmed this yet, but it's what its support team is telling customers on online live chats. See a list of Apple stores and a list of Apple-authorised service providers.
  • Your phone can't have been damaged or had unauthorised repairs. Again, we haven't had official confirmation, but Apple's support team told us: "They qualify as long as there is no accidental damage or liquid damage. There must also be no unauthorised repairs by third parties. This means that any previous repairs would need to have been performed by Apple or an Apple-authorised service provider and not a third party."
  • The cheaper replacements will be available until December 2018.

If you pay for AppleCare+ insurance or your phone is under warranty you may also be able to get your battery replaced free of charge now. You can also try asking for a free replacement battery if you believe yours is faulty – see our Consumer Rights guide for full help.

What does Apple say?

Its message to customers says: "We know that some of you feel Apple has let you down. We apologize [sic]. There's been a lot of misunderstanding about this issue, so we would like to clarify and let you know about some changes we're making.

"First and foremost, we have never – and would never – do anything to intentionally shorten the life of any Apple product, or degrade the user experience to drive customer upgrades. Our goal has always been to create products that our customers love, and making iPhones last as long as possible is an important part of that."

It adds: "Over the course of this autumn, we began to receive feedback from some users who were seeing slower performance in certain situations. Based on our experience, we initially thought this was due to a combination of two factors: a normal, temporary performance impact when upgrading the operating system as iPhone installs new software and updates apps, and minor bugs in the initial release which have since been fixed.

"We now believe that another contributor to these user experiences is the continued chemical ageing of the batteries in older iPhone 6 and iPhone 6s devices, many of which are still running on their original batteries."

iPhone 6s shutting down? You may be able to get a FREE replacement

Apple's latest announcement is separate to the free battery replacement scheme it announced in 2016 for a number of iPhone 6s models, which have been unexpectedly shutting down despite being charged.

This issue appears only to affect those manufactured between September and October 2015, though you can use your phone's serial number to check if you're eligible for a free replacement now.