I do not leave my Wifi on. I turn it off when I finish downloading what I need, but every once in a while I notice that it will get hot and the battery loses about 50% of its charge. It could be sitting at 75% and then in five minutes drop to 20%. Other times I could be using random apps to download news info for a good hour of random browsing using things like the facebook app, engadget, etc... and the charge is generally fine. Sometimes I will put it to sleep after and when I go to wake it back up, it will have less than 2% life left in it. I have the latest firmware from Apple.