The APC 450AT+ is a UPS system that requires a 6V 12Ah AGM replacement battery. The compatible Universal Power Group replacement is the UPG UB6120 6V 12AH F1 AGM Battery (UB6120), a 6V 12Ah AGM sealed lead-acid battery. This battery delivers up to 72 watts of standby power. It weighs 4.18 lb, uses F1 terminals, measures 5.94 L x 3.7 H in, and has right polarity. This is a direct drop-in replacement for the APC 450AT+ requiring no modification to the device.