accidental trolling you mean (j/k)
Phone battery is like MPG for a car. You get an estimate. If you drive on high way you get better MPG if you drive in city you get lower MPG. If you put your gas pedal to the floor too often you burn way too much gas.
Same with your phone, if you don't have screen at full brightness (because what sammyz said is 100% true) and you moderately use your phone, you'll get more out of your battery. If you are going to play games at full brightness, full volume and also downloading on 4G at the background, your battery will die very fast.
As far as I can tell your battery is fine, just remember that numbers are just an estimates.