The cord to our original Wii bar was damaged by an unknown culprit, so we went out to buy a new one. All we could find were cordless models, which seemed fine until we discovered how much they eat batteries. So, I endeavored to make it corded, using an AC adapter from my stash, until I realized, "Hey, why not USB?" When it was nearly finished, my daughter said, "Dad, make an Instructable," so here it is. I know that I left out the soldering in wires stuff, but really, it's very easy.
Here we have the victim. It uses 4 AA cells, thus somewhere around or less than 6V. USB is 5V or just a little more, close enough. At least it wont be overpowered. I dug into my stash for a spare cheap USB cable and some other wire and stuff.
Like I said in the beginning, I didn't get pics for the whole procedure. Prior to what you see here, I noticed that the connector on one of my spare wires fit right onto the negative terminal, after it had been bent upward. (Don't let the color of the wire fool you, it is a negative.) I Dremeled some notches in the plastic dividers which separate each battery section, so that the wire will go across without interfering with the battery door. The positive battery terminal was desoldered from its wire, which was then soldered to the positive USB wire, inside the housing to the left. I had removed the screws inside the battery compartment and under the rubber feet in order to access the wire. I also Dremeled a notch for the cable to exit, and crimped a piece of solid wire around the cable to keep it from pulling out.