Wait - your EVO drops only 4% charge all night? Wow! My phone drops 8-10% or so in the first 10 minutes after I disconnect it from the charger
That means something is preventing your Evo from going into sleep mode, you've got Wifi off, have got 4G on, or a combination of these conditions.
My money's on your phone not going into sleep. If you haven't already, install
Spare Parts. Then charge your phone back to 100%, unplug, and turn off the screen and leave it alone for about 10 minutes.
After 10 minutes, turn your screen back on and run Spare Parts. Go into Battery History. It should look something like this if your phone has gone into sleep mode:
If, on the other hand, the bar for "Running" is at 100%, that means your phone never went into sleep mode, even though it should have about 3 minutes after your screen turned off, if not sooner.
If you tap on the bars, you'll get slightly more details. For instance, here's the details from my "running" bar:
And even after that, my battery was still at 100% when I took the screenshots (it soon dropped down after that, of course, with the screen on and me running different apps).
If your phone never went into sleep mode, check your usage statistics, and see if you can figure out what app is preventing it from going to sleep.