I bought earlier a 910 screen, that's http://www.adafruit.com/products/910 .
The power input guide lines say 4 volts to 15 volts, as here "Power with 4.5-15VDC only into onboard buck converter". And as it happens I got it to work briefly being powered by 5 volts coming from a power supply other then the one that came with my Raspberry PI starter Kit. I believe I saw the screen light up and show the video coming into it. I then decided to swap out the plug in power supply and try a battery pack, especially since I had hoped to build a portable system concerning my system.
I stopped when I thought I smelled smoke and felt the board. It felt warm right by the coils and the regulator.
And I know that's not normal.