This video explains how to improve the battery life of your nokia by installing two simple apps

Simple Brightness:With the simple brightness app, you can keep your N900 on a low brightness for most operations and then quickly switch to full brightness for other tasks when required.


3G/2G selection applet:Another app is 3G/2G selection mode applet. Also from the status bar, you can switch from Dual Mode to either 3G or 2G. Staying at 2G helps preserve battery life.


I currently have both apps installed on my device and they really do help preserve alot of battery life.

http://www.youtube.com/watch?v=QjLIgzGG9ZQ&feature=player_embedded

just downloaded the 3g app, but the brightness one doesn't work any more

Also WiFi really kills the battery.

go to Application Manager, then "Download", wait a few minutes (depending on your internet speed etc) and you'll get A LOT of applications. By default it only shows you the finished/stable ones, but for BETAs and unfinished (yet there are a lot of good on those and some can just corrupt your phone if you install) or those who are in testing phases, you need to add new repositories which is explained here: Get access to more Maemo Application Catalogs