Apple has launched its second new repair program in one week, this time for “a very small number” of iPhone 6S models that have been unexpectedly shutting down. Phones that display the issue — reportedly only devices that were manufactured between September and October last year — will be eligible for a free battery replacement.

If you think your phone is affected by this problem, you’ll have to check for a corresponding serial number on your device at an Apple Store or with an Apple-authorized service provider — carriers that offer the iPhone 6S won’t be handing out battery replacements.

Only on devices manufactured in September and October last year

Before heading into a store, Apple advises iPhone 6S owners to back up their data, erase settings, and turn off Find my iPhone. The company also says problems like cracked screens won’t be fixed as part of the new repair service, and unexpected shutdowns on devices manufactured before or after the specific window won’t score you a free battery replacement. If you’ve already paid for a new battery because you suffered from random reboots, however, and have a phone manufactured between September and October 2015, you’ll be able to get a refund on that.