Dell power management - Battery Discharge

I have done the custom settings for battery from dell power management. I have set that the battery should start charging when it is at 50% and stop charging at 80%. When the battery has charged 80%.It has stopped charging. But the discharging of the battery is not happening itself. I have to remove the ac power so that the laptop should start using battery instead of ac power. The battery should self discharge when it reaches 80% and start charging when it reaches 50%. which is not happening currenlty. Can any suggest any solution.