Anything here helpful?http://support.microsoft.com/kb/935799
Since you asked specifically about Registry:
"How to use the registry to set the preferred power plan
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
To change the preferred power plan, follow these steps:
, type regedit in the Start Search box, and then click regedit.exe in the Programs list.
User Account Control permission
If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
Locate and then click the following registry subkey:
Right-click PreferredPlan, and then click Modify.
In the Value data box, enter one of the following:
Type 381b4222-f694-41f0-9685-ff5bb260df2e to use the Balanced plan.
Type a1841308-3541-4fab-bc81-f71556f20b4a to use the Power saver plan.
Type 8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c to use the High performance plan.
You can also type the power scheme GUID for a custom power plan that you have created. To determine the GUID for all existing power schemes, type Powercfg /List at the command prompt, and then press ENTER.
Click OK, and then exit Registry Editor."