Sorry about that. Yours and Sierra's posts ran together on me. Still, it doesn't matter because the EPS300C is the same and performs the same no matter what plane it's installed on.
If you want to use LiPoly, you need to know a few things to use of them safely, and use them without destroying them. Why not just tell you this stuff? Because it's a lot of information that is impractical to type in every time a newbie asks about LiPolys, and a lot of information to absorb in one sitting. Why isn't it on a web page somewhere? It is. The vendors who sell the cells will generally have usage, care, and feeding info online.
To properly size the pack, you need to have a rough idea of how many Amps the motor draws. A particular LiPoly can only handle so much current. Draw too much, and you ruin the cell. By combining multiple packs in parallel, they share the load.
My preferred source of Etec LiPolys is either Bishop Power Products
http://www.b-p-p.com or ParkFlyerMotors
http://www.parkflyermotors.com.