I was part of the first batch of iPHone 5's which is known to have subpar batteries...I was 14 months into it and noticed my usage was not as good as when I first got the phone.
I was around 250 cycle count and down to 72-85% full charge capacity. It was acceptable for me but wanted more juice.
I just replaced my battery yesterday and now back to 98% full charge capacity. I think just over time, the battery full charge capacity decreases.
I'm thinking I will get another 1-2 hours of usage a day with the replaced battery on 7.0.4. Hopefully even more once 7.1 is released.
Now I should be good for another year.