APC Back-UPS 520ES, 550ES 6V 12Ah UPS Battery - This is an AJC Brand Replacement This is an AJC Brand&#174; Replacement for a APC Back-UPS 520ES 6V 12Ah UPS Battery Voltage: 6V (6 Volts) Capacity: 12Ah Terminals: F1 Number of Batteries Required for a Full Replacement 2