I grabbed a couple of cheap replacement battery compartments that charge over USB from eBay over a year ago and have never had any problems.
They're only 1800mAh (although you can get much bigger) so the charge only lasts for about 4 hours but that's normally enough for me. Basically you plug the usb cable in the back of the Wiimote and BINGO! Works a treat via either the PC or Wii although I tend to recharge using the PC just in case charging via the Wii on standby causes problems. I'd recommend these over a charging station cos they still work fine with covers on the remotes (I just made a small hole in the cover for the cable) If you have a cover on the remote they tend not to fit in those Nyko-style docking stations
