Dear Carlos, glad to hear that you flew GWS Beaver and safety landed without battery pack!
When over power with 8 Cell, AAA, 9.6Volt, NiMH, 720mAH, Sanyo. I like to suggest you to add on second wing support strut on both sides of wing.
I guess your hard loops really "hard" enough to sweep battery out!
Very possible to cause the wing bent!
Wish you can fly her safe! GWS will have a pair of floats for her soon!