pm-powersave is a utility to manage the power-saving configuration of the computer when it is connected to the AC and when it works on battery. You should make the changes you desire to the pm-powersave config files (for AC/Battery respectively). You can find more information about the issue here.
In my case, as I want to save as much energy as possible in both cases (AC/Battery), I copied the files from
/etc/pm/power.d and edited them to always work like in battery mode. At the end of each file, functions are called in depending of the received value (true for battery and false for AC). So, I replaced all AC function with the ones for battery. Then I added the script in the link above, with some modifications (not so aggresive) and replaced again the AC function calling with the Battery one.