When I first got my GS4 my battery life was terrible and charging took forever. I took it back to the Sprint store where I bought it and they have a battery load tester to test batteries. They tested my battery, found it was bad and opened a brand new GS4 box and gave me the battery out of that box. No problems since and I have actually been impressed with the battery life compared to previous smart phones.
Take it back to where you bought it from and see if they can help you out. This is why I always buy my phones at a local store...I've bought all my phones over the past 15 years from two local stores and I they always take care of me.