Tech giant Apple is offering to replace the battery of certain iPhone 6s models free of charge after a fault was detected that means some smartphones unexpectedly shut down despite still having significant remaining charge. We tell you how to check if your handset's affected and how to get your replacement.

The problem seems to be affecting iPhone 6s models – excluding the iPhone 6s Plus – manufactured between September and October 2015. You have three years from the original purchase date of your iPhone to get your free replacement battery.

Apple has said that owners of a faulty iPhone 6s will need to go into one of its stores or an authorised service provider to check if their handset is eligible for a free replacement battery. However, we've found out the list of qualifying serial numbers so you can check yourself.

What's the fault?

Certain iPhone 6s devices may unexpectedly shut down despite showing a significant amount of charge left on the phone – some users have reported their phones shutting down at 20% or even 40% battery life.

Apple has confirmed the problem is not a safety issue and only affects a "limited serial number range".

Nevertheless, the Apple-authorised repair centre we spoke to said such replacement programmes usually only take place when a significant number of devices are thought to be affected, and that a fair few customers had already got in touch about it.

How do I check if my handset's eligible for a replacement battery?

iPhone 6s handsets manufactured in September or October 2015 are those likely to be affected, so if you bought yours around that time then you may be able to claim a free battery replacement – though it's worth bearing in mind that the manufacture and purchase dates aren't always very close together.

Apple says you'll need to go into one of its stores or an 'Apple Authorised Service Provider', but after speaking to one of the centres on the phone we were able to check if a handset was eligible, as well as get a list of qualifying serial numbers.

To check yourself if your phone is eligible for a battery replacement: go to Settings > General > About on your iPhone, and your serial number should be listed.

If it contains any of the following combinations as the fourth and fifth characters, your phone should be eligible for a replacement battery:

Q4 | Q5 | Q6 | Q7 | Q8 | Q9 | QC | QD | QF | QG | QH

Apple wouldn't itself confirm the qualifying serial numbers, though the repair centre we spoke to was confident this was the definitive list.

It's worth checking yourself with Apple before making a trip to a store – after speaking to a senior advisor at customer support (0800 107 6285 – free from landlines and mobiles) we were able to confirm a particular serial number qualified the relevant phone for a free battery replacement. Alternatively, you can call your local repair centre.

The replacement programme is intended for models of the iPhone 6s with the specific battery issue mentioned above, though one repair centre told us that any iPhone 6s with a qualifying serial number is covered.

My serial number's not covered and/or I don't have an iPhone 6s, but I'm still having battery problems – can I get a replacement?

Unfortunately this replacement scheme only covers specific iPhone 6s devices, not any other type of iPhone. If you're having other battery issues on another Apple device, you'll need to contact its technical support as usual (and if you're out of warranty you may be charged for any repairs).

Apple offers free battery replacement for faulty iPhone 6s handsets – how to check if you're eligible
Apple offers free battery replacement for faulty iPhone 6s handsets

How to get your free replacement battery

First things first, before getting your battery replaced, make sure you back up your iPhone to iCloud or iTunes, turn off Find my iPhone and erase all your data (go to Settings > General > Reset > Erase all Content and Settings).

There are three different ways in which you can get your battery replaced:

  1. Book an appointment at an Apple Store (click 'service'). How long this takes will depend on availability, though someone here at MSE Towers was able to get their phone back within four hours of their appointment.

  2. At an Apple Authorised Service Provider (click 'service'). Mobile operators' stores are not part of the scheme, only authorised centres. How long it takes will depend on the centre; the one we spoke to quoted a turnaround of seven to ten working days. Call ahead to make sure the battery replacement service is available on the day you plan on visiting.

  3. Log it with Apple Support (or call 0800 107 6285). If you can't get to a store or service centre, you can arrange for your iPhone to be collected by a courier for a battery replacement. This can take five to ten working days.

Note that if your phone has any other damage which impedes the replacement of the battery, such as a cracked screen, these will need to be fixed before the battery can be replaced. Apple says in some cases you may be charged for those repairs.

Can I claim a refund if I've already paid to have my iPhone 6s fixed?

Apple says if you believe your iPhone 6s was affected by the described battery issue but you've already paid to have it repaired, you can contact it about getting a refund.