Here is a post I read from Apple community, have you got the same issue?
I know this may seem ridiculous but after having updated my iPhone 6, 64 GB to iOS 8.1.3, yesterday January 27, I noticed my battery isn't lasting anywhere near as long as it was before this.
Usually the way I use my phone by 5pm every evening, I have at least 65 - 70% battery life, today I'm at 44% and know for sure I've used it less than usual, which is why I came here.
I want to thank everyone who replies in advance.