A stiffening capacitor is an extremely large value electrolytic capacitor. Capacitors have the ability (capacity) to store a charge on their "plates". The larger the capacitance, measured in units of Farad, the greater the charge a capacitor can store for a given voltage. Most automotive capacitors can store a charge at 10 to 20 volts, and are rated from about .5 Farad up to 20.0 Farad or even more. Capacitors have an extremely low internal resistance to current flow, much lower than that of a battery. Capacitors can therefore charge and discharge power much faster than a battery can.