The new Apple iPhone 6S and 6S Plus are displayed during an Apple media event in San Francisco, California, in this file photo from September 9, 2015. [Photo/Agencies]

Consumers' query about smartphone's mystery power-off

US tech giant Apple Inc on Dec 2 announced the reason behind an abrupt shutdown problem that recently affected some users of the iPhone 6s.

"We found that a small number of iPhone 6s devices made in September and October 2015 contained a battery component that was exposed to controlled ambient air longer than it should have been before being assembled into battery packs. As a result, these batteries degrade faster than a normal battery and cause unexpected shutdowns to occur," a statement posted on Apple's official website said.

The company also explained in the note that this was not a safety issue.

The statement was released after China's consumer protection watchdog - China Consumer Association (CCA) - issued a query letter earlier to ask the company to explain and provide solutions to malfunctions reportedly found in iPhones.

According to the CCA, many consumers continued to complain after Apple announced a free battery replacement program for iPhone 6s users, claiming that the abrupt shutdown problem also exists in iPhone 6, iPhone 6 Plus and iPhone 6s Plus models.

On Nov 21, Apple introduced a free replacement program, to resolve recent reports of the unexpected shutdown of the iPhone 6s.