I had 4G turned on overnight as well (where I have full 4g/3g service). I've heard that leaving 4G on while in a 3G-only area will drain the battery, but hopefully that problem will be fixed with an update.

> From what I remember (and I may be mixing up phones here)

You don't, but it's not entirely correct: from the early review, the Evo had a bad battery life (as in, noticeably under average for the category), and if 4G was turned on it went from bad to utterly terrible.