Hey, My friends easy start batteries for his revo keep running out rather quickly, I was just wondering if you could use a 12 volt gel cell battery from my starter box? Would this fry the motor or anything else... Or would it be ok?

No, it will fry the electronics in the wand and possibly the motor. If his battery is dying too soon then get a different battery with a higher mAh rating. A 3000mAh battery will last roughly twice as long as a 1500mAh one. Also, be sure that his charger is fully charging the battery. Some of the chargers that came with Traxxas vehicles tended to under charge batteries.

ahh ok, thanks