Almost every “my phone has got slow and it dies by teatime” is a battery, not a phone. The processor has not aged. The screen has not aged. One consumable part has worn out, and on an iPhone it is the cheapest part in the device to put right.
Before spending £799 on a replacement, spend twenty seconds checking whether you need one.
Check the number first
Open Settings, tap Battery, tap Battery Health. Two things matter there.
Maximum capacity is what is left of the original. Apple’s published design target is 80% of original capacity at 500 complete charge cycles for iPhone 14 and earlier, and 80% at 1,000 cycles for “iPhone 15 models” — Apple has not updated that wording for the 16 or 17, so read the higher figure as applying to the recent phones and check it yourself if it matters. A cycle is a full charge’s worth of use, not a plug-in: two half-days is one cycle. Five hundred cycles is therefore about eighteen months of charging every day, and considerably longer if you do not. That last sentence is our arithmetic, not Apple’s.
Peak Performance Capability is the slowness. In Apple’s words: “As your battery health degrades, so can its ability to deliver peak performance.” On iPhone 6 through iPhone XR, iOS actively manages performance peaks once a worn battery has caused an unexpected shutdown, and the Battery Health screen says so in plain words when it has. That is the mechanism behind a phone that feels sluggish for no visible reason, and a new battery removes it.
What Apple UK charges
Out-of-warranty battery service, from Apple’s own pricing widget, retrieved 20 August 2026:
| Model | Battery service |
|---|---|
| iPhone SE (2nd and 3rd generation) | £65 |
| iPhone 11, iPhone 12, iPhone 13 | £85 |
| iPhone 14, iPhone 15, iPhone 16, iPhone 16 Plus, iPhone 17, iPhone 17e | £95 |
| iPhone 16 Pro, iPhone 16 Pro Max, iPhone 17 Pro, iPhone 17 Pro Max, iPhone Air | £109 |
Every row above is a model we selected and read on the day. Pro and Plus variants are priced separately from the base model of the same generation, so check your exact model rather than reading across.
Apple’s own caveats, verbatim: prices are for “out-of-warranty service from Apple and will be subject to VAT. A delivery fee may be added if we need to send your device. Apple Authorised Service Providers can set their own service fees and will provide their own estimate.”
Check the warranty before you pay anything. Apple states that its one-year warranty “includes service coverage for a defective battery, in addition to rights provided under local consumer laws”, and an AppleCare plan extends that. A battery that has failed rather than simply aged may not be a bill at all.
The arithmetic
An iPhone 13 with a tired battery costs £85 to make whole. A new iPhone 17 is £799 from the Apple UK store. The battery is 11% of the price of replacing the phone, and it fixes the specific thing that is wrong with it.
The honest way to think about the payback is in cycles rather than years. A new battery resets the count to zero, so it should last roughly as long as the first one did — if the original gave you three years before it annoyed you, the second one will do something similar under the same treatment. Three more years for £85 is £28 a year. Three years of a new £799 phone is £266 a year, and buys you a faster chip you were not complaining about.
When it is not worth it
The phone is out of security support. This is the one that overrules the arithmetic. A £85 battery in a phone that has stopped receiving security patches is £85 spent on making an unpatched device last longer. Check what your model is actually still receiving before you book anything — Apple’s security-releases page lists every update and the devices it went to, and our answer on iPhone update lifespans explains why the “supported” tables you will find elsewhere are answering a different question.
There is a second fault. A battery is cheap; a battery plus a screen is not. Apple UK’s screen prices on the same widget run £219 on an iPhone 11, £289 on an iPhone 12, 14 or 15. Add £85 or £95 for the battery and a two-fault repair on an older phone is £300 to £390 — into the range of a good refurbished newer model with a warranty on it. One fault, fix it. Two, do the sum.
The damage is not itemised. Apple’s “other damage” tier — £369 on an iPhone 11, £405 on an iPhone 12, £539 on an iPhone 14 — is what water ingress and internal failures land in. At those prices you are buying most of a phone.
Apps have already outgrown it. If your banking app has started warning you about your iOS version, a new battery buys you endurance you will not get to spend.
The short version
If the phone is on a supported iOS, has no other faults, and Battery Health is the thing you are unhappy about, replace the battery. It is £65 to £109, it addresses the actual complaint, and nothing else you can buy for that money improves a phone as much.
If it is out of security support, or if something else is broken too, the battery is money spent propping up a decision you have already made.