Mine has the .46 ax and I had to put my 1800mah 4.8v flat pack as far foward as it would go, but still right under the cockpit. It still balanced just slightly tail heavy, but this is the way I like it to fly. The .46ax runs great but barely has enough power to hover with a 12.25 X 3.75 prop. While it would probably be fine for relaxed sport flying, I don't think I would like this plane with a .46 La. The .55ax would probably be my first choice for this plane if staying with a two stroke.