4 AA is all you really need if you are only dealing with one wii mote. The Wii-mote takes 2 batteries, and you can just leave the other 2 in the charger and swap them as necessary so you never miss a beat. I play my Wii a few hours every day, but it takes weeks before I need to change the batteries.
I have this charger thing that plugs into the wall socket and it only holds 4 batteries and it will only take AA and AAA, but that works out fine because I only use it for the Wii. I do have a separate charger which is much larger that can charge size C and D, but I almost never need those kinds of batteries. Really, what uses that size? Not much...