The  L-3 Avionics PS-835D is a power supply which provides continuous standby power for self-contained gyro horizons and essential flight instruments. The PS-835D Emergency Power supply is designed as a 24 VDC (nominal) emergency power source for prolonging the operation of a connected standby attitude indicator when the aircraft main power bus has de-energized. The aircraft main power bus provides trickle charging to PS-835D while the aircraft performs normally. During a power failure, The PS-835D batteries take over supplying power to essential instruments without interruption. The output of the PS-835D can be subsequently converted using either Avionics Systems Model SI-100( ) Static Inverter of the SC-841 Static Converter to provide power for standby indicators of different power requirements. The SI-100 provides output of 115 Vac or 5 Vac, 400 Hz either at single or three phase alternating current. The SC-841 provides direct current outputs of 2.0 to 6.5 VDC (user adjustable).

The PS-835D Emergency Power Supply is fully enclosed unit, designed to easily mount onto an existing avionics shelf or the optional mounting rack Avionics Systems Model MTG-101, with models available with lightning surge protection. The face of the unit provides individual cell monitor LED's, voltage output monitor LED's, battery Heater Operation Monitor LED's, and a battery test switch. The PS-835D is 14.11 inches in length, 7.774 inches in height, 2.40 inches in width and weighs 13(8 for A,C,E) pounds. The PS-835D's operating altitude is from sea level to 55,000 feet at 25°C. The PS-835D needs an operating temperature of -55°C to +70°C. Models A,C, and E use 2.25 Ah cells while models B,D,F, and G use 5.0Ah cells. Models C,D,E,F,and G are current models while models A and B are considered obsolete but can be modified to a current model.