Iphone 6 plus battery

Hi everyone ! I am currently using Iphone 6 plus 64gb from past 8 months and I have problem with it's battery life. Though apple claims 24 hours talk time on 3G and 12 hours of internet browsing. But in my case this is not true even for half of the time mentioned. I did voice out this issue at one of the apple store and talked with genius bar team. They simply checked the health of my battery with a mere software which apple claims to be able to detect battery problems , but I am not sure a software is able to find out possible hardware faults and is 100% full proof. They are not ready to replace my phone and I feel cheated. This is my first apple phone and the kind of service I receive is not satisfactory. Plus there are no proper hierarchy to complain regarding the apple store. I would never suggest anyone further to buy apple nor do I will. I am already looking to sell out my phone because the battery issue is really frustrating and most of the times it drops down 2% each. Like if right now my phone has 25% battery showing up and in some time just being idle you can see the phone battery will directly go down at 23% without being at 24%. Knowing all these they are being ignorant and not ready to help. I really want to voice out this issue to all Customer relations guys at apple that is this how you give your after sales services. I have never has such experience with HTC or Nokia before. They are really good at maintaining customer relations. What should I do in this case ?