iPhone 6 battery Issue

I have problem with the battery for my both IPhone 6 and IPhone 6 Plus.

the iPhone 6 battery drain fast and doesn’t last for 12 hours,

and iPhone 6 Plus doesn’t starts, I’ve already changed the battery twice before but still have the same issue.

could you please advice me what to do?

the Apple Store in Cardiff closed for few month refurbishment and the closer store it’s in another city that’s two hours away.

I heard that all iPhone 6 user should claim a compensation because of the battery faulty on all iPhone 6. Is it true and how to make a claim.

thank you