The following solved it for me....
To do it via the Power Options, right click the battery icon (or electrical plug icon) in the lower left corner of the screen, then...
1. Select a power plan and then click "Change plan settings"
2. Click "Change Advanced Power Settings"
3. Look for "Processor power management" and expand it
4. Expand "Maximum processor state"
You can now enter the percentage usage of the CPU while on battery and plugged in.
Note that it does not work the way you think it would work. Meaning if you set the CPU to 90% it will run at 90% of the stock clockspeed. No... it's not like that. For example, my i5-2410m has a stock speed of 2.3GHz. Turbo boost overclocks it to as high as 2.9GHz when stressed.
100% = Turbo Boost on.
99% = Turbo Boost off. CPU runs at 2.3GHz
78% - 98% = 1.796GHz
69% - 77% = 1.596GHz
60% - 68% = 1.397GHz
So you get the picture.