i know you need cap and battery.. a cap is a device that charges up (calculated in farads or micro/pico/nano farads for small caps) and then discharges when needed... you wire it in parrallel with your battery (positive to positive, negative to negative) and allows your battery to put out higher CCA (cold cranking amps) basically means that under short/snap periods of high current drain (amplifier while heavy bass beat) the voltage won't drop...