There are no safety issues involved in Apple's battery replacement program, according to a statement on the company's China website.
Apple has offered replacement batteries to qualifying iPhone 6S owners after a small number began to shut down unexpectedly. But as of now, there seems to be no risk of repeating the Samsung Galaxy Note 7 debacle, where phones were recalled on risk of catching fire.
Instead, a battery component used in September and October 2015 was exposed to air for longer than usual in the iPhone 6S models, triggering a feature that causes the iPhone to shut down automatically under certain conditions, such as extreme cold.
While Apple has said the battery issues only affect a small number of iPhone 6S users, others have also complained. Most notable? Tony Fadell, who helped invent the iPhone and currently owns an iPhone 6S Plus.
There have also been isolated reports of fires connected to iPhones, although there's no evidence these incidents are widespread.
"We looked for any other factors that could cause an iPhone to shut down unexpectedly. After intensive investigations, no new factors have been identified," Apple said. "We will continue to monitor and analyze customer reports."