[Dragon2]

Every so often its good to wipe your battery stats and start from scratch. To do this you must have bootloader unlocked with a recovery image like ra recovery etc.

1.charge phone full
2. Turn off phone, hold down vol down and power till bootloader comes up, use volume down to scroll down to recovery and press power to select it.
3.scroll to wipe and select it using trackball
4. Scroll to wipe battery stats and select it.
5. When done, power down phone and charge for a while after its green...
6. (Optional ) I also after that use it till it completely dies, then charge again full from 0 to 100...
That should do it and hopefully get some more life out of your battery if your having some bad battery times...