read this thread:
or this thread:
I'll repeat my obeservations again:
For the gamecube, god battles are stackable. See Pixelate's post for the effects when you equip multiple god battles.
My test was using the special attack on a double cannon several times with two hunewearls. We tested 1 god battle vs 2, 3, and 4. Each had a significant difference.
If you don't believe me I suggest you test it yourself somehow. I would take video for you but unfortunately my character is MIA.
Finally, despite the stackablity of the god battles I never have more than one, I would suggest using other units instead.