Always be 100% bright when I'm using battery

When I'm using battery only - Ubuntu turns in some mode, when If I do not use my PC for about 5-10 seconds - the screeen becomes darker.

Where do turn this option off? Because I often need to read (without pressing keys and moving my mouse) and I can't see with dark screen.

Solution 1:

11.10

Open System settings. Then, click the Screen option, and uncheck the Dim screen to save power box:

And you're done!

11.04

Open gnome-power-preferences - to do that, hit Alt+F2, then type in gnome-power-preferences. You'll see something like this:

Go to the "On Battery Power" tab, then you'll want to make sure that the "Reduce Background Brightness" box isn't checked:

That should do the trick.