Hey there, SRanjha.
This is most likely caused by the power options set for your power plan when the laptop is not with a plugged in charger. This means that in order to save power and make your battery last longer - you get a decreased performance. Click with the right mouse button on the battery icon in the bottom right corner of your laptop (next to the clock) and select Power Options. When you open it, you'll see 2-3 predetermined power plans and you can either edit them with options preffered by you, or just select the one which you'd like to use. Most likely you'll see 3 plans - Balanced, Power Saver and High Performance. Try choosing High Performance while the laptop has no charger plugged in, to see if that changes the...