There are many simple steps and some more complicated steps but in the end, I was able to achieve an 8 hour charge on my year old laptop. The results will vary for your laptop if you have an inefficient CPU or a high RPM hard drive the gain will be smaller, but generally you will gain more time out of one charge.
In some cases, following these steps can even extend the life of the battery. Which means savings of 100 dollars or more.
The laptop used in this instructable is a HP Pavilion DV5130ca
2.0 GHz - AMD Turion 64
120 Gigabyte 4700 rpm
Broadcom 802.11b/g wireless adapter
128 mb ATI Rage Mobile
Windows XP MCE 2005
All other specifications are insignificant when configuring a PC for power management.
Step 1: Start Simple
1. Reduce the brightness of your monitor to the lowest readable level.
The backlight in most laptops are like "mini-fluorescent" (cold cathode) bulbs. They will really drain your battery quickly.
2. Turn off your wifi when you do not need it.
The wifi card is another power hungry device. Think of this - when you make a call on your cell phone, the battery drains very quickly, but if you simply play games or listen to music, it can last a very long time. This is the same idea. The wifi card is "calling" the hotspot all of the time. Even if there isn't a hotspot around, it is continuously looking for one.
3. Use windows primitive power management to control your CPU.
When unplugged from the wall, click on the battery in your task bar and click max battery. This will extend your laptop's life because your CPU will be reduced to a slower speed. (continue reading for a better explanation of reducing your CPU's speed as this makes a HUGE difference in the length of your battery charge.)
4. Unplug unnecessary peripherals.
Unplug that USB light or your wireless mouse when you don't need them. Although minor, these devices could give you those extra few minutes of charge.