Unplugged power at 5pm yesterday, worked on it up to 1130pm last night, and as of this post the Surface RT still has battery power. I'll let it run in battery mode until I get the flashing warning.
Sent from my Windows Phone 8S by HTC using Board Express
Update:
5pm yesterday, removed from charger
up to 1130pm yesterday, browsing, download, games (2 hrs)
up to 8am today, stand by
up to 10am today, downloading
up to 1115am today, playing music
... 26% remains as of this post.
I think I've said enough.
Update:
It finally shuts down... 1:54pm my time.