Apple has launched a new replacement program for its iPhone XS, XS Max, and XR smart battery cases, after charging issues were discovered in some devices. According to the company, some of the cases may have a problem where they won’t charge when plugged into power, or may fail to charge your iPhone. If your model is affected, then Apple or one of its authorized service providers will replace it free of charge.

At $129, the battery cases aren’t cheap, but their tight integration with the iPhone means that they come with a few advantages. iOS will display the charge level of your battery case in its top notification bar, for example, and it can also pass data through the battery case’s Lightning port. If your case is eligible for a replacement, then it might be worth taking it into an Apple Store regardless of whether it’s having problems. You’ll get a newer model, and there should be less chance of it developing problems in the future.

According to Apple, the affected models were manufactured between January and October 2019 (the cases were announced in January). If you want to take advantage of the program, then Apple says you’ll need to take it into an authorized service provider or an Apple store, where it will be examined to make sure it’s eligible. If it is, then Apple says it will dispose of your old model in an environmentally friendly way. Affected cases will be covered for two years following their original sale, according to Apple.