Bit of a bump but my launch day iPhone 7 Plus has been chewing the battery up badly recently to the extent that when I took it off charge yesterday, within an hour it had dropped by 10%. The battery health was showing at 91% with coconutBattery showing around 400 cycles.
I was passing an Apple store today so popped in. I had to wait three hours to be seen as I didn't have an appointment and then they said that I may not notice any difference with a new battery because the drain on their support/diagnostics looked normal. I said I'd like a new one anyway so an hour and a half later I was £25 lighter and I have a replacement battery. There was no argument when I asked for it, they were quite happy to fit it but did make the point (repeatedly) that I may not notice any difference.
It's nice to have a battery with a cycle count of zero