Rotor Riot did a thing on flying with Lipo batts and radio gear not too long ago. IIRC the batteries were a carry on item. I reckon the biggest hurdle is convincing the TSA goons that it's not a food item. A big Lipo does look like a block of Velveeta, which, as we all know, is the TSA rubber-glovers' favorite snack after a long hour of cavity searching and tush groping.