Find out what the spec for the motor AND the esc on that plane are. It's rather important.

Why do you want to put a 4S battery pack? Just remember that there are more considerations than the voltage rating of the pair to deal with. If this is a serious increase in voltage from the original setup, you really have to be concerned with torque limitations.

I had a small three channel plane that came with a two cell pack but offered a three cell as an option. I had both and flew it with the two cell pack and it flew ok, but was not exciting enough. So, I put the three cell on without thinking about it and hand-launched the plane at about half throttle. When airborne, I pushed the throttle to full and heard this strange noise and watched the plane flutter to the ground. When I walked up to it, I noticed that the wires leading from the ESC to the motor were tightly twisted around the shaft that held the motor mount in place and tore the ESC out of it's mounting position and right up against the base of the motor - it was mounted using velcro. Nasty. The motor was a throw away, by the way.

CGr