If it was like that since you bought it, you should take it where it was sold to support it.
If the use was degraded the battery life my recommendations are:
- Close background applications that you do not use frequently.
- Deactivate the functions that do not use like Bluetooth, NFC, location or GPS, Zone wiFi.
- Turn off automatic screen brightness and set it manually when more or less brightness is required.
- Uninstall battery savers or battery coolers.
- Uninstall personalization applications that work with animations, such as animated backgrounds or animated widgets.
- Review in Settings> Applications> Running, and stop the applications you have not requested to run. EYE: Do not stop those that work with the Operating System.
- Disable updates with mobile data, recommend upgrading app with Wifi, or do not allow updates (doing them manually will allow better control).
- Charge it with your own charger.
- Do not leave it charging more than the time necessary for full charge.
Tell us how you did.