Its ok to use a car, to jump start a quad, ...provided the motor, on the car is not running. If its running, the alternator will put out up to 15 volts, and that is what leads to problems. If the car is off, then its only 13.2 or so volts, and the quad is used to that and there wont be a problem.
Its like, you can plug your tv into a 110 volt 10 amp outlet, or a 20 amp outlet, neither one will hurt the tv, because the internal resistance of the tv will limit the amount of current coming in. But if you plug the tv into a 220 outlet, itll explode. Its the volts thatll wreck stuff. The electrical equation is current=volts divided by resistance. So if the volts are higher... the amps will be also.
Just trying to help here,.... a 12 volt battery is a 12 volt battery, just because it can theoreticaly put out 850 cold cranking amps, doesnt mean it will . The internal resistance of the starter will limit the current, to what is needed.

Just remember....the car must not be running.