Hi Nick,
I am Dave, I will help you with this.
In Windows, you can only set one Power Plan, there is no option or even a registry hack to set a separate Power Plan on battery power.
The best power plan to use is balanced, that will let Windows automatically ramp up the power of your processor... etc. when required by resource hungry operations.
Also, turn on Battery Saver Mode, by clicking the battery icon on your taskbar, that will throttle down your laptop when it is on battery power.