The issue cropped up because some batteries supplied to Apple were exposed to ambient air longer than their usual time. This leads to them degrading faster than usual and cause random shutdowns of the device. The replacement program was only for a small set of iPhone 6s units that were manufactured between October to November 2015.
Apple is already running a repair program for the iPhone 6 Plus for the ‘Touch Disease’ in which it is replacing display units with non-functional touch or screen flickering issue for $149. iPhone 6 owners have also complained about their device randomly shutting down irrespective of the charge left, but it is unclear if the issue is as widespread as it is for the iPhone 6s owners or is simply being caused due to the age of the device. As of now, it is unclear as to why Apple would be considering extending the free battery replacement program from the iPhone 6s to the iPhone 6.
Are you noticing any battery issues on your iPhone 6 that could lead Apple to potentially launch a free battery replacement program for it? If yes, drop a comment and let us know about it.