Good day all. This was one of my simplest hacks ever. My wife and I each have an Evo 4G and as you may know there's no affordable portable charging solution for these things.
Summary: 4 D-Cells, meet my wife's and my Evo 4Gs. Kthxbye.
I grabbed a project enclosure, 4x D cell clip, and a tiny protoboard from Radio Shack. Then I stole two USB ports from some garbage lying around. A little quick-and-dirty work ahead gave me a portable box that should charge both Evos almost 50 times. It charges them quickly and the unattenuated 6V doesn't seem to be a problem -- the wall chargers included with the phones pump out 5.7V anyway. The total cost was about $25 plus 1.5 hours; I was surprised by how many tools I needed to use, though. The protoboard is held in place by one screw and a carefully placed twist tie.
Notice the busted USB port (missing its inside clip). I pushed a drill right into it when cutting the hole in the lid. A few minutes of surgery with the stats reshaped the connectors to work well even without the white plastic support. Just be sure to plug the cable in the right way or I'll have to perform the surgery again
Lesson learned: mark it and take it apart before you drill even with a drill press.
I figured I should share this with my fellow hacking nerds because a LOT of devices will handle the 6V input pretty well, especially if they come with chargers that take a wide input range (so think, almost any premium smart phone). And I give this a 1/10 or maybe 1.5/10 in difficulty -- even a newbie could do it, and seriously the pictures should be enough to get your own up and running. Just remember to back out the screws and clip them to the appropriate length so there's nothing pokey around.
~ dan ~