Four hours of battery time on a Linux laptop

I previously wrote about reducing CPU usage for Firefox by disabling Firebug. Later, I wrote on disabling the YSlow extension also reducing CPU usage.

Now, the laptop is able to exceed 4 hours of battery time under Kubuntu Linux 12.04:

Four hours, seven minutes:

09:37:27 localhost pm-utils: Power source switched to battery, Battery: discharging, A/C adapter: off-line
13:44:15 localhost pm-utils: Power source switched to A/C power, Battery: charging, A/C adapter: on-line

Four hours, fifteen minutes:

12:40:49 localhost pm-utils: Power source switched to battery, Battery: discharging, A/C adapter: off-line
16:55:02 localhost pm-utils: Power source switched to A/C power, Battery: charging, A/C adapter: on-line

The above is the output of a custom script that detects and logs power events.

Note that this is not the usual 6 cell 4,400 mAH battery, but the larger 9 cell 6,600 mAH one.