The Aritech PM844-A is a 230 V AC input, 12 V DC / 4 A switch-mode power supply with a 0.5 A battery charging output, sized for a backup battery up to 18 Ah (type BS131N). The metal enclosure houses two status LEDs indicating mains and battery condition. Typical application is 12 V DC supply for intrusion, fire and access-control systems requiring standby battery backup.