Have you updated the firmware? One of the things that is much improved is battery life. I can get 24 hours off charger with ease (granted, 8 of it I am asleep) with the current firmware.

I suggest you update it. And turn off wifi if you want maximum battery life.

(re battery life, guess you've never used an iPhone 3G, or any phone made by HTC, with sub 8 hour battery life?)