Take a look at this:
http://www.rcgroups.com/forums/showthread.php?t=508443
Someone made a nice writeup on how to re-make these packs! This person used a Milwaukee V28 battery, but it uses the same cells as the Makita pack linked in the first post.
According to this, each cell is 3000mah (I've read it's more like 2900mah).
My 4s 6600mah 8C battery seems to have developed a bad cell... Maybe it's from when I dropped the pack (slight bulge at the end), but I'm not sure. It doesn't hold its voltage well after a few days. Last week, I found the cell (actually 3 cells in parallel) at 0.08v! I was able to charge it back up at a SLOW rate using the NiMh charge mode, and got it past 3v, at which point I set it to the Lipo charge mode. After that, any slight ballooning there may have been all but disappeared. A few days ago I discharge the cell to about ~3.8v, and today it is at 3.75v, which is very good. I'll use that pack carefully and hope that the bad cell works out all right, but I think I'll be purchasing a couple of the Makita battery packs :). I'll take them apart, and make 4 groups of 2 cells in series. I've attached a picture to show how they'll be set up. You can see 8 cells. The gray curves represent sub-c battery bars, black curved line is a jumper wire, blue lines are wires that will go to a balancer connector, and the red/black lines are obvious. This is probably the easiest way to do it for most RC cars that use dual battery packs.