go to
www.allelectronics.com and look under batteries and click under subcategory Lithium-ion and they have a battery pack with two AA Li-ion cells in it for $6.50
all you have to do is crack open the case they are inand there you go. Plus they have a charger for it for $4.50 but you would have to modify it to charge our cars. There is a whole bunch of things there for cheap at thrt site.