Apple published a statement which hopefully will address customers' concerns about reduced performance of older iPhones.
"We’ve been hearing feedback from our customers about the way we handle performance for iPhones with older batteries and how we have communicated that process. We know that some of you feel Apple has let you down. We apologise. There’s been a lot of misunderstanding about this issue, so we would like to clarify and let you know about some changes we’re making."
apple.com/uk/iphone-battery-and-performance
To regain the trust, Apple is reducing the price of an out-of-warranty iPhone battery replacement to £25 for anyone with an iPhone 6 or later whose battery needs to be replaced, available worldwide until December 2018. Details will be provided soon.
Please bring your iPhone for diagnostics and get your battery replaced for £25.