You might have seen this article already but if not, its worth reading because its highly relevant to UMPCs.

15-ways to extend your battery life. It includes tips like ’Dim your screen’ and “Hibernate not standby.’ 

My extra tips are:

Browsing is CPU heavy. If you’re just reading text on a website, try using the RSS feed if they have one. It can cut CPU usage considerably by avoiding all the processing power needed for flash, animated GIFs and javascript. Using an offline reader also means you can pick up all the news and then turn off the WiFi, which brings me to the second tip…

Turn of WiFi as much as possible. If you can connect via your mobile phone using Bluetooth or a USB cable, do it! In some UMPCs this can save up to 20% of battery drain. Again, try using offline tools (email client, RSS reader) to save on WiFi usage.

Screen dimming is very important. In an idle UMPC, it can save 20-30% depending in the screen type.

Kill those background tasks. I use Spybot Search and Destroy’s advanced features to keep my XP startup list as slim as possible. If you’re using Vista, optimise it!

Use power-saving modes but don’t slow yourself down too much. Some power-saving modes are extreme. The VIA-C7 locks down to 400Mhz in battery saving mode and it can really slow down the workflow.

Via jkOnTheRun