Take on the iPhone battery

Every iPhone goes trough that period when it goes from a well oiled machine to a basic brick. It happens both gradually and suddenly as the battery slowly starts to deteriorate and one day it just sucks. This happened to me this week, basically I can barely make it through my hour bus ride commute on one charge, by the time I get to work the phone is sputtering and of course as with any iPhone, there is nothing you can do about it.
Why is he most frustrating is how quickly the battery leek drops. One minute it's 68% then it is 32% and then it just turns into a black screen