Your 7.2 at a 60% charge doesnt have enought Mah available to cycle your rifle. Charge the battery and try it again.
My suggestion is you use at minimum an 8.4 1100.
The reason why it's getting hot is because you're still trying to cycle power through the rifle, altough there's not enough power to cycle the weapon so the power is going to the motor, the motor tries to spin, but can't, and it heats up...
Intellect makes good batteries... 8.4 1600's for cheap on Ebay.