As noted by the program's dedicated webpage, Apple discovered a "very small percentage" of iPhone 5 handsets may suffer from unexpectedly short battery life due to an unannounced issue presumably related to manufacturing.
According to Apple, iPhone 5 units affected by the problem come from a batch sold between the product's launch in September 2012 through January 2013.
Owners who purchased their handset within that time period and are experiencing shortened battery life symptoms can check if their unit is eligible for replacement via Apple's website. A serial number is needed to process the request.
As with past replacement programs, users with affected iPhones will be required to take their handset in to an Apple Authorized Service Provider, Apple Store or send it off to Apple for examination prior to service in order to verify eligibility.
Aside from determining whether an iPhone contains one of the known-faulty batteries, the phone must be in working order to be eligible for a part swap. Any damage that would make replacement of the battery difficult, like a cracked screen, would first need to be fixed, meaning the swap-out could come at a cost.
For now, the initiative is limited to users in the U.S. and China, though coverage will be expanded to other countries on Aug. 29. Apple is extending the program to users with affected iPhone 5 batteries for two years after first retail sale or until Mar. 1, 2015, whichever provides longer coverage.
The program's start comes just weeks before Apple is expected to reveal a next-generation iPhone lineup on Sept. 9.