I have said this a thousand times, but multibillion dollar companies never listen to me :(
Rechargeable AA batteries >>>> Rechargeable inbuilt batteries
If you need to be able to charge more batteries at once with an AA battery charger, get another one, in Australia they retail for $0 anyway (ie bundled with batteries for the price of the batteries)
It shouldn't be too big an issue, though, because as people have pointed out, everyone has a wii and will use that to charge, or you can fork out for a usb hub or charge from your pc