I couldn't figure out why my phone kept eating my battery in a matter of hours. I was about to go exchange it for another when I figured out what was going on. When you open the factory browser with the default Google homepage it fires up your GPS to put your location up. I'm guilty of opening the browser, doing what i need, then telling it to close which it never does. Instead it re-opens the browser and goes back to your home page which for me was the default Google page. I would hit that back soft key quickly hoping to stop it from loading the page and thus, in my mind at least, closing the browser.
What happens though is the browser keeps the GPS turned on attempting to find your location. If you re-open the browser it will go ahead and locate you and turn off the GPS but if you hit that back key before it locates you the GPS keeps trying to locate you until you open the browser back up allowing it to finish the task or until it kills the battery, whichever comes first.