There's a lot of things you can do to conserve battery, if you don't need to the speed try to limit your data settings to HSPA+ instead of LTE, I'm not sure how that's done on AT&T variants, but there should be something in the network settings. Also turn off NFC if you don't use it. Install CPU Spy and see if your phone goes into Deep Sleep mode when it's just idling by. If it's not going into that mode you have a rogue app thats keeping it awake thus killing battery.
If you've rooted/flashed your phone there'd be a lot more you can do but that may screw with your warranty.