After you have discharged the capacitor due to heavy power draw, the capacitor will need to recharge. How does it recharge? Well, the capacitor sits in between your battery and your amplifier. Once the capacitor is discharged, it will attempt to charge itself by drawing power from your battery. Then, when the amp needs power, the capacitor will supply current from the battery as well as any “extra” current it has saved up. Once its discharged, the vicious cycle continues.
Most common car audio capacitors are rated at 1 farad, while I’ve seen some reach as high as 5, 10, 20, and higher. No matter how high the rating, a capacitor will still hamper performance. This is because capacitors cannot supply the needed current for any extended duration of time. When your amplifier needs current, it will suck the capacitor dry in less than one second, leaving your capacitor to use your battery to charge up again. Once the capacitor is charged, that extra current can then be transferred onto the amp.
See where I’m going now? If a capacitor can only hold a charge for less than one second, while drawing substantial amounts of current from your battery in an attempt to charge back up while delaying power the amp, then what is the point? There is none. Capacitors are known in the car audio community as a marketing ploy to make people think they need something, when in reality, they really don’t. Take your money and invest it in a second battery. A capacitor these days runs between $50-$80. Add a few more dollars and you can get a second battery, which will supply your amplifier with much more power than a capacitor ever could, while not straining your electrical system.