Replace the battery cover, put the bar on top of the TV, and plug the USB cord into the Wii. Viola, no more batteries! These things come in differen...
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.