On the two I've got with .40 La's on them, I ended up shoving some foam into the fusalage, aft of the servo tray to make a nest for the battery and shoved the battery back into the hole. Using a square futaba 600mah battery. Had to trim a little off the header that the rudder and elevator push rods run thru so the battery could slip in and out, but this got my Cg back where I wanted it without adding anymore weight. Its working pretty good so far. The one I've got with a Magnum .46 still required some weight on the tail.