Apple found “a very small number” of iPhone 6s devices are unexpectedly shutting down and the firm will issue a battery replacement free of charge to eligible users.

“This is not a safety issue and only affects devices within a limited serial number range that were manufactured between September and October 2015,” it said in a statement.

If users have experienced issues they can visit an official store and have their phone’s serial number checked to confirm eligibility for a battery replacement.

Wireless carrier partners are not participating in this programme.

If the device has damage, such as a cracked screen which impairs the replacement of the battery, it will need to be resolved prior to the battery replacement.

Apple also said it may restrict or limit repair to the original country of purchase.

If users believe their iPhone 6s was affected by this issue, and they paid to replace their battery, they may get a refund.

Just last week, the China Consumers Association said it was investigating complaints that some iPhone devices – 6 and 6s – were suddenly shutting off even when half their battery life remained. However, Apple said the problem is only with 6s.

The 6 Plus isn’t without issues though as recently some devices were found to have the “touch disease” – the touchscreen becomes unresponsive.

Apple claims this only happens after the phones are dropped multiple times on a hard surface and then incur further stress.

It told users if their iPhone 6 Plus is exhibiting these issues and is in working order, and the screen is not cracked or broken, Apple will repair it for $149.