RC battery as airsoft battery?

I have an AK 74, and I wanted to try being a support gunner. I remembered that I had 3 9.6v RC car batteries, all large connector. My AK is mini connector. Not a problem, I pulled the connector off another RC car battery. So now i have 2 connectors on my battery pack. The pack works in a 4.8v rc car, but not the gun. Likewise, the gun battery (8.4v 1500 mAh) won't turn the motor on the car. Are the batteries wired in opposite polarities or what? They're both NiCd batteries.