$ gsettings set org.gnome.settings-daemon.plugins.power 'use-time-for-policy' 'false'
made it possible to run my netbook for several minutes without AC (I didn't bother trying longer), and dconf-tools and experiment show this setting is persistent across reboots.
The only drawback for me was that I couldn't reboot without AC; my netbook hung on a blank screen.
I finally found a workaround in this thread: http:// ubuntuforums. org//showthread .php?t= 1866533 . Specifically,
$ gsettings set org.gnome. settings- daemon. plugins. power 'use-time- for-policy' 'false'
made it possible to run my netbook for several minutes without AC (I didn't bother trying longer), and dconf-tools and experiment show this setting is persistent across reboots.
The only drawback for me was that I couldn't reboot without AC; my netbook hung on a blank screen.
Good luck!