Apple says that the limited stocks of this period will shift many interventions until March-April with regard to the battery replacement on the iPhone 6 Plus. Delays also expected for other models.
In a note shared internally today, Apple writes that replacement batteries for iPhone 6 Plus are scarce and will not be available before the end of March or early April in the United States and the rest of the world. For iPhone 6 and iPhone 6s Plus, however, the wait is two weeks. No problem for iPhone 6s, iPhone 7, iPhone 7 Plus and iPhone SE.
Users who are interested in replacing the battery on the iPhone 6 Plus, iPhone 6 and iPhone 6s Plus will therefore have to wait between two weeks and few months, depending on the model in their possession. The problem is probably due to the huge demand for replacements, after Apple lowered the price to $29 in response to criticism for having linked the decline in iPhone performance to batteries that are starting to deteriorate.
Recall that the replacement program at $29 is valid until December 31, so unless you absolutely need an immediate replacement of the battery, the advice is to wait a few months before bringing your iPhone for assistance.