Apple once again faces mounting complaints from Korean customers, this time for a lack of stock to replace faulty iPhone 6s batteries.

Apple has been offering new batteries for free of charge to users with a problematic iPhone 6s devices, which shut down at random points, since Nov. 21, local reports said Sunday.

A growing number of customers, however, are reporting cases of inconvenience over the shortage of batteries at Apple authorized service providers and wireless carriers.

“My phone turns off unexpectedly, so I visited an Apple authorized service center to receive a new battery. But workers there told me that they are out of inventory. I don’t understand why Apple Korea made the announcement without making sure whether it has enough stock,” 28-year-old Irene Lee told The Korea Herald.

Apple Korea was not available when called for comment.

Recently, Apple Korea has dealt with complaints over sloppy customer service, for posting on its Korean website details about how to exchange faulty batteries only in English on Nov. 20. It provided a translated version four days after the initial post.

Apple Korea is currently advising customers to visit stores after Dec. 8, when additional stocks are set to reach Apple authorized service providers and wireless carriers.

Confusions over which iPhone 6s devices are eligible for exchange is also adding on to the frustration.

“This is not a safety issue and only affects devices within a limited serial number range that were manufactured between September and October,” according to Apple Korea’s website. The announcement fails to specify which serial numbers it is referring to.

iPhone 6s users have to call the Apple call center to find out whether their devices are eligible for replacement.

Apple has been listed in the top 15 ranking for ignoring consumers’ complaints for five consecutive years, the state-run Korea Consumer Agency said.

The battery replacement program follows an official request made by the China Consumers’ Association to Apple for a look into unexpected shutdown issues of iPhone 6s and iPhone 6 devices.

By Kim Bo-gyung (lisakim425@heraldcorp.com)