I usually switch my system to "Better Energy Savings" while on battery. It kept switching back to "Custom." I ended up tracking the problem down to a program called "SmartSleep":http://www.jinx.de/SmartSleep.html. It appears that it was changing my settings to Custom about every 30 seconds or so:
de.jinx.SmartSleepDaemon SmartSleepDaemon: setting hibernation state to: 0
If you are wanting to get the best out of your battery life while not connected to a power source, you might want to disable "SmartSleep":http://www.jinx.de/SmartSleep.html.