Iphone6 battery drain after updating IOS 9.2

Hi there

So this is a very big deal to me and it was not the first time to begin with, i contacted apple multiple times all they did is suggest things i already did and ran Diagnostics & Usage from their part. They pretty much told me everything i knew about my problem and did not help.

I bought this Iphone6 on June/2015 time i did not have an issue till i updated to IOS 9.2 that is when i noticed my phone had a battery issue example. when i leave it at a 100% charge at night go to sleep wake up 6 hours later the phone drops to 40% sometimes i find it at 10% when i forget to close applications.

Trust me i have tried everything out there my warranty is expired and i will not buy another iPhone so i would have the same issue over again. I owned 2 Iphones in my life and both had the same issue with the battery after updating IOS .

Kindly suggest any other form of fix out there