Hixx, definately let me know if you can get the plastic bolts and wing straps.

The 8 cell nicd pack that came with my Magister has a one inch square piece of velcro on the fronf of it and the corresponding velcro piece was on the front of where the battery slides back into the fuselage. Maybe back just 1/2 " from the front. Has held the battery with no issues. I usually just push the battery in about flush with the opening. CG must be fine as if flies well. You may want to make sure your CG is good and that the ailerons are moving as far as they are supposed to. Just some ideas.
Have you range checked your transmitter? I recently had some issues with a JR6102 and have switched to the Spektrum DX6.

Carl