Apple is offering a free battery replacement for iPhone 6S smartphones that keep shutting down abruptly. The issue was reported last week by a Chinese consumer protection group, which was found in iPhone 6S handsets manufactured between September and October last year.

Apple has officially confirmed that the problem is limited to a handful of iPhone 6S smartphones with a particular serial number range. The company further adds that it’s not a safety-related issue, and suggests the problem is fixed by replacing the battery which the company is offering free-of-cost. However, the iPhone maker did not reveal how many iPhone 6S handsets were affected and in which region.

Apple was asked to check some iPhone 6S smartphones that were automatically shutting down, which happened when their battery level was between 50-60 percent. Users who believe their iPhone 6S is unexpectedly shutting down are advised to backup their data on iCloud or iTunes, switch-off ‘Find my iPhone’ feature, and delete all their files and photos in order to get their battery replaced. Also, users who think that their iPhone 6S was affected by the battery issue and have already paid to get a replacement, can contact Apple to to enquire about a refund.

In other related news, Apple has also started selling refurbished iPhone 6S and iPhone 6S Plus models at its certified online store in the US. These refurbished iPhones also come with a one-year warranty, just like what you’d get when you buy a new one. Besides, they also come unlocked, come with a new battery, along with an outer body shell. You can pick-up the refurbished 64GB rose Gold iPhone 6S Plus at $589, while the 16GB Silver iPhone 6S Plus can be purchased for $529. Meanwhile, the 16GB iPhone 6S is available for $449. Interested users can buy refurbished iPhones at Apple certified online store here