Comment by Joe_Cool

Brightness down, LAN card disabled (the media sense on RTL cards sucks about 1.5W with no cable plugged in, wtf? Thats more than the Wifi needs)

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.