Apple issued a press release: https://www.apple.com/iphone-battery-and-performance/
See this:
Apple is reducing the price of an out-of-warranty iPhone battery replacement by $50 — from $79 to $29 — for anyone with an iPhone 6 or later whose battery needs to be replaced, starting in late January and available worldwide through December 2018. Details will be provided soon on apple.com.
I would think the CGA would likely cover us here in NZ.


