iPhone 6S battery lasts for 2.5 hours only! Want to know the replacement process

Hello,

Since last 1 year i am using iPhone 6s, and now from last 20 days i am facing battery backup issue. My iphone was in warranty when i lodged the complaint but on 18th DEC it expired. I lodge the complaint before 2 week ago before the expiry.

Firstly, i went to authorized apple repairing center, where they diagnosed my phone and kept it for observation for 48 hours. They said system showing that my battery is OK and iPhone is working fine but after all the diagnose nothing has changed my iPhone's battery is still working in same manner and lasts for 2.5 to 3 hours. Again i went to the repairing center to get the issue resolved but they said battery is showing "OK" status and we can't help you in this. Contact the apple care.

After this i contacted the apple care, via chat and call, they suggested me many troubleshooting methods but none of them worked for me. My battery still lass for only few hours. I am fed up of this thing. I want it to get replace as it was in warranty when i lodge the complaint and all the troubleshoots suggested by the tech-support team not working for me.

I have attached all the evidence for showing iPhones inefficiency.

Please help me guys! i am still connected with the technician and she only suggested me silly troubleshooting methods which are not able to fix my problem.