I just googled it and there is a problem with the iPhone 6 and 6 plus but not until around 600 recharges when it loses 20% of its storage capacity. However, Apple have issued a replacement battery kit but the phone has to be sent away to be done
Well I am guessing its not every one .....and from experience ( on laptop) Apple are quite quick with any repairs
I am convinced
I think I may buy outright then find a service provider
Now to find the cheapest one
It will have to be the 6 plus