This is G&G have told me that the gun has to have 11.1v as anything else is not powerful enough  
  
" 
Thanks for your mail. 
  
The most recommended Li-po battery is 11.1V with three piece or any other 11.1V Li-po which could be put inside this model. 
We have received some feedbacks regarding no fire while pulling the trigger with 9.6V Ni-Mh or 7.4V Li-po battery as we recommended on manual. 
Then we found it needs much power to run the motor pushing ETU system, even 9.6V Ni-Mh battery works, it will be out of power soon. 
Therefore, we have revised the note on our manual and recommend 11.1V Li-po battery on our ETU models." 
  
So i need to make a 11.1v fit :/