Could you confirm, the iFly only draws 600 milliamps max? At 12V, that's only 7.2W, which seems a little low to me (but I'm no expert in current consumption for small electronics!).
If true, that's good news. I'm thinking about cobbling together a homemade rechargeable battery pack, and it seems like 8 2500mah AAs in series might provide a reasonable runtime for me, depending on battery performance and iFly voltage tolerance.