After trying to install Windows 8.1 from MAPS directly on the Surface Pro, I had a big scare with the battery warning. After one of the many reboots, I suddenly started receiving a black screen with a white icon indicating that the battery was critically low.
I left it plugged in overnight and tried again in the morning and still had the same indicator. I then decided to completely drain whatever was left in the battery so I left it unplugged and headed out for the day.
When I got home, hit the power button firmly prepared to see the same warning or to have the battery be completely dead. To my surprise, it came back to life completely and booted Windows as if nothing had happened. Windows was even reporting that the battery was full.
I’m not sure why I got the “battery critical low” warning or why it suddenly started working again, but letting the Surface sit for a while did the trick and brought it back to life.
See Surface RT and Surface 2: Windows won’t start or stops responding for more troubleshooting help. This article specifically references the Surface 2, but much of it applies to the Surface .