iPhone users have been using battery cases to extend the battery life of their phones for years, but Apple has recently offered its own versions of these accessories.

A number of Apple-made battery cases sold in 2018 has exhibited problems, and the company has launched a program to replace customers' faulty battery cases for free.

Apple determined that some Smart Battery Cases made for iPhone XS, iPhone XS Max, and iPhone XR may experience charging issues. An affected Smart Battery Case may exhibit one or more of the following behaviors:

• Battery case will not charge or charges intermittently when plugged into power
• Battery case does not charge the iPhone or charges it intermittently

Affected units were manufactured between January 2019 and October 2019. Apple or an Apple Authorized Service Provider will replace eligible battery cases, free of charge.

Affected products include the Smart Battery Cases for the iPhone XS, the iPhone XS Max, and the iPhone XR sold between January and October of 2019. Appla said no other iPhone Smart Battery Cases are part of this program.

Apple clarified that this problem is not a safety issue; that's a necessary clarification, given that there have been battery-related issues with other gadgets that were safety concerns.

To replace an affected battery pack, you can go to the Apple Store or make an appointment with an Apple Authorized Service Provider. The case will be inspected to check if it's eligible.

Apple also notes that the replacement program does not extend the warranty for these battery cases. Cases are eligible for replacement, the company says, up to two years from when they were purchased.