w3m can even display images in a linux console if you have the proper drivers or use KMSCON. It unwieldy but surprisingly usable. And my laptop battery runs for 8 hours which is quite amazing for a Zen1.
I imagine your display is almost entirely black for the majority of the time, with your (most probably) LCD backlight blasting away, trying its hardest to get a few thousandths of its light output through the few pixels on the screen that it can escape! XD
And powertop (great piece of software, thanks Intel) tuned to the max + powersave scheduler. All that on Windows or KDE results in about 4-5h of battery though. So fbdev must be somehow really frugal.