For those of you who are running Windows RT 8.1 Preview on your Surface RT, you might have experienced an issue where your battery would drain out quickly. This is a known issue and Microsoft has offered a temporary workaround until the final version of Windows RT 8.1 is released.
"Since installing the Windows RT 8.1 Preview I have experienced high battery drain in Connected Standby. I'm losing 2-3% an hour when the Surface RT is in standby, so losing 30% battery during the day when not being used," one user stated on an official Microsoft support forum. The issue stems from a Bluetooth setting in Windows RT 8.1 and Microsoft is aware of this issue.