don't really know anything about batteries other than what i have read on the forum. if you go with the lithium ion ones they should be the (protected type). if i understood it correctly this will keep them from exploding during recharging. here is the link to the ones that were recommended from another post. http://www.dealextreme.com/details.dx/sku.5790

these batteries need to be charged with a charger designed for lithium ion batteries. here is the link to the charger that was recommended in that same post. http://www.dealextreme.com/details.dx/sku.1251

Edit: the 18650 are not interchangeable with AAs