I have a Surface RT device (the original) and absolutely love it. I use it every day. However, one of the challenges I have been dealing with was after the upgrade for Windows 8.1 came out, I noticed the battery is always dead when I picked it up. Before, I could go 3 to 5 days between charges, depending on how much I was using it. Now, it would discharge in standby within 24 hours!
To track this – you can create a Battery Report. Open an elevated command prompt on the SurfaceRT device, and type in:
powercfg /batteryreport
This will save an HTML file as seen above.
This is a pretty cool report that will show some interesting statistics about your batter. But it will also show your periods of use, and how much the battery drains during connected standby:
In the table above, I can see I entered standby at around 9pm on the 17th, and when I picked it back up around 4pm the next day, the battery was almost dead! The chart in the report shows this as well, pretty cool:
What's the fix???
If you look on this page: http://www.microsoft.com/Surface/en-US/support/hardware-and-drivers/battery-and-power
There is an interesting section at the bottom:
Surface RT only: Battery issue when updating from Windows RT 8.1 Preview
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:
Step 1:
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.)
Step 2:
In the search box, enter command prompt.
Step 3:
Touch and hold (or right-click) Command Prompt to bring up the context menu. Tap or click Run as administrator.
Step 4:
On the User Account Control dialog box, tap or click Yes.
Step 5:
At the Administrator: Command Prompt, enter the following:
powercfg -setdcvalueindex SCHEME_CURRENT 19cbb8fa-5279-450e-9fac-8a3d5fedd0c1 12bbebe6-58d6-4636-95bb-3217ef867c1a 3
Step 6:
Then enter
powercfg -setactive scheme_current
Voila…. this fixed mine immediately. And yes, I did update from 8.1 preview to the full release of 8.1. My surface can now sit in connected standby mode for an entire day and only consume about 10% of the battery life. 
