Apple has admitted that a “small number” of iPhones have a fault that makes them unexpectedly shut down.
The iPhone 6S phones affected by the fault were made over a two-month period last year, the tech company said in a statement.
Users have found that the phone will stop working, despite the battery being charged.
Apple said: “This is not a safety issue and only affects devices within a limited serial number range that were manufactured between September and October 2015.”
They added: “If you have experienced this issue, please visit an Apple retail store or an Apple authorised service provider and have your device’s serial number checked to confirm eligibility for a battery replacement, free of charge.”
The offer will not be valid at mobile providers.
At first, the problem was linked to battery manufacturing but the firm is still investigating the cause.
The battery replacement offer comes just days after Apple announced a similar scheme to repair a fault in the iPhone 6 Plus, which caused the screen to become less responsive over time.
But that fix came with a price tag of £146.
Just weeks ago, Samsung had to recall and stop production of the Note7 smartphone after several incidents of the device exploding and catching fire.