The applet is called 3G/2G/Dual Mode Selection Applet and you can download it from the App Manager on your phone or from there: http://maemo.org/downloads/product/M...ection-applet/

Your battery life seems not quite right though. Battery life on the N900 is terrible but 7 hours with almost no use seems extreme. I'd get around 15 hours with the usage you describe. There has been a few threads here that gave suggestions on how to make battery life on the N900 a bit less miserable. You might want to do a search (use the Power Search option on the right side bar).

For me, the two biggest battery drainers have always been the email client (CPU usage goes through the roof whenever it checks for new emails - setting it to check for new emails every 30 minutes instead of every 5 minutes helped a lot) and the IM client (don't use it anymore).