We've had our Wii for a few years now.
We currently have a controller dock that charges from the Wii USB, but it's really fiddly getting them to sit on the dock meaning they are rarely charged when needed. After all the faffing I think I'm just gonna get some nimh AA batteries.
What does everyone do for Wii batteries?
Hybrio or Eneloop AA's are the way to go.
I normally buy a 24 pack of Duracell on eBay every couple of months for about ?6 delivered that does the job.
rechargable AA's. Good to have loads of spares and a decent charger though as some of the cheaper ones I have can go flat very quickly, saying that I have had some batterys since my first digital camera, so they must be getting on a bit.
15 pack rayovac for a buck at the dollar store.

Never have a problem with them.
I can highly recommend Energizer AA rechargables. It came with a USB charger that has been great for my 360. They have lasted five times longer per charge than the xbox play and charge kit.