I updated from 8.1 Preview to 8.1 GA. Running the powercfg commands listed here
Microsoft Surface RT and Surface 2 battery and power | Recharge Surface seems to have fixed the problem. I figure it'd be worth a shot whether you can from Preview or not. I'll report back after having doing more testing.[h=3]Surface RT only: Battery issue when updating from Windows RT 8.1 Preview[/h]If you updated Surface RT from Windows RT 8.1 Preview to Windows RT 8.1, you may notice a decrease in battery life. During the update, the wireless adapter power policy isn’t migrated. Instead, the power policy is set to a default value that consumes more power both during use and in the connected standby state.
To restore the wireless adapter power policy to the correct settings, open an administrator command prompt:
[TABLE="class: px"ordered-steps-table""]
[TR]
[TD]
Step 1:[/TD]
[TD]Swipe in from the right edge of the screen, and then tap
Search.
(If you're using a mouse, point to the lower-right corner of the screen, move the mouse pointer up, and then click
Search.)[/TD]
[/TR]
[TR]
[TD]
Step 2:[/TD]
[TD]In the search box, enter
command prompt.[/TD]
[/TR]
[TR]
[TD]
Step 3:[/TD]
[TD]Touch and hold (or right-click)
Command Promptto bring up the context menu. Tap or click
Run as administrator.[/TD]
[/TR]
[TR]
[TD]
Step 4: [/TD]
[TD]On the
User Account Control dialog box, tap or click
Yes.[/TD]
[/TR]
[TR]
[TD]
Step 5: [/TD]
[TD]At the
Administrator: Command Prompt, enter the following:
powercfg -setdcvalueindex SCHEME_CURRENT 19cbb8fa-5279-450e-9fac-8a3d5fedd0c1 12bbebe6-58d6-4636-95bb-3217ef867c1a 3[/TD]
[/TR]
[TR]
[TD]
Step 6: [/TD]
[TD]Then enter
powercfg -setactive scheme_current[/TD]
[/TR]
[/TABLE]