I have a Acer Aspire One AOA 150 with Windows Xp Home and Windows 7 Pro with a 3 cell battery. What are the techniques for improving battery life in both Windows7 and Xp ?
No matter the OS, the main issue with laptops and notebooks is the backlight - lower it as low as possible.
Next, close background processes you do not need - The Atom CPU is much better than desktop CPUs however, the higher the utilisation, the higher the power draw (marginal).
Set good power management techniques, hard drive power down etc.
If using XP, it is a bit harder to set additional items, however in Windows Vista and 7 go to the power management control panel (or press Windows Key+X to go to mobility centre) and you can change the power mode which will automatically set best practices for different situations.