Hi Sidney, the 4S pack will probably get it off the ground just fine. A 5S pack would get you closer to the voltage that the plane was originally designed to fly on, but the LiPo pack should way significantly less. With either a 4S or 5S LiPo replacing the two NiMH packs, you'll want to double check you center of gravity closely to make sure the plane isn't tail heavy before trying to fly it. Good luck and good flying!