By default Ubuntu GNU/Linux powers on all of your Mini 10's hardware devices at boot, and perhaps this is the way it should be. But if you want to squeeze some extra time out of your battery you can benefit greatly by disabling some of these after you have booted into your Gnome Desktop Environment.
One piece of hardware that I have noticed to take a large bit of energy is the SD Card Reader. It seems to pull around .5 Watts. I never used an SD card in my life, so it makes no sense for me to have this piece of hardware enabled while I am out and about. To disable it, go to System > Administration > Disk Utility. You will see the SD Card Reader listed in the device tree. Highlight it and click on the "stop" button up top to power it down. That should allow you to save a little more battery.
If anybody knows of another way to turn this device off, or perhaps avoid turning it on at all I would appreciate a point in the right direction.
Now, it may help for you to have some way of analysing power consumption with a little more accuracy than is provided on the battery icon on the panel. For this you can use a program called powertop. You can find powertop in the Ubuntu package repositories. Find it in Synaptic and install it. You may start it with "sudo powertop". (Note: This utility requires that it be run as a superuser.) It will collect data for 5 seconds and then start up. From within the program you can see what processes and hardware devices are taking up the most energy. It will also give you an approximation of the Watts your computer is pulling, and a time estimate for battery life in the current configuration. Even more, it will provide suggestions for improving battery life and allow you to make the necessary changes with the press of a key.
Another important aspect of power management is processor speed. By default Ubuntu will set you CPU clock speed to an "on-demand" setting. This means that Ubuntu will try to keep your clock speed down, but when it notices that a certain program could use more power then it will increase the clock speed to full. Since I am never doing anything very CPU intensive while on battery I can safely have Ubuntu limit my clock speeds to the minimum necessary. There are two ways that I know of doing this; through Gnome, or via command prompt. I will explain the Gnome way.
Right click on your top panel and choose the "Add to Panel..." option. You will be presented with a window and several applets to choose from. Scroll through the list until you find the "CPU Frequency Scaling Monitor" applet. Add it to the panel. Now, do it again. The CPU on the Dell Mini 10 uses a technology called Hyper-Threading, all this means is that the CPU is virtually split into 2 CPUs. So in order to limit the CPU's total clock speed you will have to set CPU0 and CPU1 to the appropriate settings. Now that you have both of these icons on your panel you can right-click on them and set the clock speed to "Powersave" mode. Remember to do this to both CPUs.
The command line method uses a program called "cpufreq-selector." If you are interested in doing it this way then you are probably familiar with man pages. I'll leave you to it. It is worth noting however that there is a bug in this program (or perhaps somewhere else in the system?) that causes it to hang instead of exiting properly. It's mostly a nuisance and can be worked around by a simple ^C.
I have at times gotten approximations of about 8 hours of battery life after taking these steps. This is of, of course, with the 6-cell battery, the screen display brightness at the minimum setting, wifi off, and the computer idling. While engaged in light computing (IE: playing nethack, or writing/editing text in vim) I can pull about 7 and 1/2 hours. This is a welcome change from my old laptop which would give me about 45 minutes if I were lucky.
What I have yet to figure out is a way to turn off USB devices. According to powertop they are culprit to numerous wake-ups and the Webcam seems to be on 100% of the time. If I could find a way to disable these USB devices I am sure I can wring out another good chunk of power usage. Does anybody have any ideas on how to do this?
That is all the information I have acquired on the subject. I hope that someone will get something out of this. And if anybody has some more info on this, or perhaps some answers to my questions, I would be happy to hear from you.
PS: I am running Ubuntu 9.10 on a 10v with, as previously stated, a 6-cell battery.