On Friday afternoon, Apple opened up an iPhone 5 battery replacement program after discovering that a “very small percentage” of units “may suddenly experience shorter battery life or need to be charged more frequently.” The iPhone 5 was originally launched in September 2012, and Apple says that the affected units were sold between that month and January 2013. Apple’s support website includes a tool to check if your serial number belongs to a faulty iPhone 5. The replacement program is available at Apple Retail Stores, Authorized Apple Service Providers, and via AppleCare. Apple tells eligible iPhone 5 owners to backup their data, Turn off Find my iPhone, and Erase all Content and Settings before coming in to have the battery system replaced. Apple says it won’t repair phones with other problems like cracked screens. If you’ve already paid to get your battery fixed (and you’re eligible for this replacement), Apple is offering refunds.