|Clean out your browser's Cookies, History, Temp Internet Files, etc.|
Do a disk clean up.
Run msconfig, go to the Start Tab, and uncheck all except Microsoft and your antivirus program, Apply and restart the machine.
[It sounds like your browser or system is loaded down and/or too much is running in the background. When you unplug it is trying to throttle back to conserve power when on battery and there is just too much going on.]
Restart in Safe Mode with Networking, download, update, and run Malwarebytes to make sure you do not have an infection of some type. Remove all it finds.
Check your power settings to be sure that it is not too restrictive when you are on battery. Take care in resetting these or you will have a short battery run time.
You have to be a little bit crazy to keep you from going insane.
---- Save Big Bird -----