The Hewlett-Packard Model 5085A Standby Power Supply provides uninterrupted regulated 24 volts dc at a 2-ampere rated output. With the internal batteries at normal (60%) charge, the Model 5085A has a standby capability of 14 ampere-hours at +25°C. A r eserve-char ge feature permits charging the batteries to full capacity, providing 21 ampere-hours of standby power. The Model 5085A is designed to be rackmounted; hardware necessary for rack installation is supplied with the instrument (except screws for attaching to rack). The Standby Power Supply consists of: 1) ac-to-dc supply; 2) battery supply regulator; 3) output voltage regulator; 4) standby storage battery; 5) relay and indicator circuits. When operating from ac line voltage, the supply provides regulated 24 volts dc to the load and charging current to the standby storage battery. When ac power is interrupted, the battery immediately supplies power to the load, the relay switches, and the AC INTERRUPT light indicates the interruption of line power. When ac power to the Model 5085A resumes, the circuits automatically return to the original condition of supplying the load and charging the battery, except that the AC INTERRUPT light remains on until manually reset by pressing the RESET button. Normally, the internal battery is charged to 60 per cent of its ampere-hour capacity. The internal Normal Charge/Reserve Charge switch enables charging the battery to full capacity.