Why Does Phone Die Faster When Not Being Used?

[music_man185]

I just got my s7 Friday night. I was on it much of the weekend. I was very impressed with the battery life. At one point, I had 2.5 hours of screen time and was only at 50%. Today being Monday, I went back to work and was not on it near as much. This evening, the screen time is less than 1.5 hours and I'm almost at 50%. This is the same problem I had with my note 3. Battery was much better when actually using it. At work, I have no signal. So all day long, my phone is on airplane mode with wifi enabled. It makes sense to me, that my battery would be 10x better being on airplane mode and not hardly using it all day. What am I missing? I don't have hardly any apps, that I can think of, that would be trying to sync all day.