If it was that way since you acquired it, you must take it to where it was sold to you for support.
If with the use it was degrading the battery life my recommendations are:
- Close applications in the background that you do not use frequently.
- Deactivate the functions that you do not use like Bluetooth, NFC, location or GPS, Wi-Fi Zone.
- Deactivate the automatic screen brightness and set it manually when more or less brightness is needed.
- Uninstall battery savers or battery coolers.
- Uninstall customization applications that work with animations, such as animated backgrounds or animated widgets.
- Review in Settings> Applications> Running, and stop applications that you have not requested to run. EYE: Do not stop those that work with the Operating System.
- Disable the updates made with mobile data, it is recommended to update the app with Wifi, or not allow updates (doing them manually allows you better control).
- Charge it with your own charger.
- Do not leave it charging more than the time necessary for full load.
Tell us how it went.