Li-Ion Power Tool cells work great for RC!

[MetalMan]

David, the best way to use them is to remove their casing and basically break the pack apart like you would with a cheap stick pack and then rebuild it like you would a cheap stick pack. The only difference is that they aren't NiMh, but Li-Ion. BTW, they really aren't that heavy. For the same weight as 12 NiMh cells, you can get a 4s2p (14.8V, 6000mah, 90amps continuous) pack, and be able to charge it in 20mins if you had a good enough charger (it would require 18amps!).
On Ebay you can buy the 7 cell version that uses the same cellsk. They are sold as the replacement batteries for Milwaukee power tools.