Picked up a Aero Technolgies Ultamate 300 Bluehawk in a swap for 10 A123 cells. Orininal owner had a problem with it when the instructions called for a CG 2 1/4 to far back. It ended up a tail heavy dog. I found it took 10 oz of lead to bring the CG in. No way, lead in models is against my religion. What to do? I found that if I made up two 2 cell A123 packs they would fit nicely under the cowel as far forward as they could be. No easy to get into or out of the model so I will build them in with charge/balancing jack accessable to connect to a CellPro charger. This will give me a 30 minute charge capability and since there is no recorded incident with A123 cells I feel reasonably safe leaving them in the model. It appears now that the CG is going to be right where it belongs.