G5 5587, slow performance on battery

My dell G5 is almost not usable on battery. Not able to play movies, songs over Bluetooth speakers, etc properly. I have already selected "High Performance" settings on battery in Power Plan but still, CPU gets slow to 798Hz from 3989Hz. Please help me out of this. I have also tried to change the processor power management in advance power settings on the battery to 100% percent but still, CPU is running very slow, sometimes reaches to 2GHz but most of the time it stays on 798Hz.