"The agency is well aware of recent iPhone issues and is taking a close look at it," an unnamed KATS official told The Herald. While KATS hasn't officially launched an investigation, it wants to make sure the problem isn't like the Galaxy Note 7 battery issue, which caused devices to randomly catch fire and start smoking. The agency is currently in talks with Apple Korea about the issue.
In November, Apple launched a repair program for iPhone 6s devices experiencing the unexpected shutdowns, saying that "a very small number of iPhone 6s devices" that were manufactured between September and October 2015 were affected. Apple said the problem was "not a safety issue."
On its Chinese website, Apple said the shutdowns were caused by a manufacturing error where some batteries were overexposed to "controlled ambient air," causing them to degrade faster than normal. In addition to its repair program, Apple now lets you check your iPhone 6s serial number to see if you're eligible for a new battery.