The size of use-able "AA" batteries are:
Diameter 13.7 - 13.8 mm
height 42.5 - 49.3 mm
The size of those batteries are too large. I know from first hand, I brought 3 sets and boy was I upset until I built my 1/24 ford focus (now I have a 6 cell monster). After some searching I found a site (from another thread).
http://www.slavin4u.com/lithium.html
They use paypal but they also have other methods. I got mine from a camcorder case. Radio Shack also has them but too expensive($14 each) and they're non-rechargable!