Those look pretty cool, and also pretty effective. Although I think I'm just gonna stick with Alkakline or NiMH. With the 7.2 V mod I did it is already faster than I need it to be and it only has the stock motor in it. were you thinking of adding the two 4 V cells or the smaller voltage cells? if you are going to add the two 4 V, then I suggest you try the 7.2 V mod first since mine is already faster than you could ever need in a race (unless your going for pure top speed
).