Rockville RXC4D 4 Farad Digital Car Capacitor Blue LED Voltage Display Power Cap Rockville RXC4D 4 Farad Capacitor 4 Farad/12 Volt Stiffening Capacitor with 24 Volt Surge Capacity Lucite Encapsulated Display and Logic Circuitry. Red LED Digital Voltage Display. Blue Led Flashing Charge and Discharge Metering.