iphone 6 plus just turns off with 60% battery life???

iphone 6 plus currently running IOS 8.1.2 i hardly update my phone as you can tell lol. however i am recently having problems with my battery and battery life. its very inconsistent, it will charge to 100% no problem and as of the last two weeks or so it has been depleting rapidly. having to recharge multiple times a day when in previous months it would last thew whole day with heavy usage. know in the last week or so it has been acting like the iPhone 5 battery problem, with just shutting down without warning its not hot and once i plug it in to charge back up it powers up very quickly not acting at all like a depleted battery. as it powers up its back to 60% or whatever it was when it suddenly shut down. im not sure what to do i called and talk to apple phone support and they set me up an appointment and told me to hard reset and if it doesn't help then show up for he appointment.

well after the hard reset the function of the battery seemed better in all honesty so i cancelled the appointment, so here we are and now back to the same issues only days later. im worried that if i take it in there to them to see that they will somehow try to tell me it was caused by me in someway (I.E. water damage) only from previous experience with the iPhone 3g. im not sure what to do, I know i have limited time on the one year manufactures warranty will this help me in any way? thanks in advance for all the help 😀