When Reddit users and a Geekbench developer discovered and shared that Apple's approach to mitigating the aging of batteries is partly responsible for the gradual performance degradation that iPhone users have sometimes experienced, Apple made an effort to explain its choices. The company promised to add software features to give users "more visibility into the health of their iPhone’s battery" and offered a discounted battery replacement program: new batteries for affected devices will be just $29 through the end of 2018. That means users could reclaim some of that performance.
However, an Apple Store memo obtained by MacRumors suggests that owners of the iPhone 6 Plus in some regions (including the US) will have to wait until March or April to replace their batteries. According to MacRumors' report, Apple believes its supply of batteries for these devices will not meet demand in the beginning of the year.
Other models are not expected to see such significant delays. For example, the iPhone 6 and 6S Plus are expected to take around two weeks to become available to customers who purchase them, and batteries for all other affected iPhone models should have a quick turnaround time.