Units operate up to 40 hours on a standard 9-volt alkaline battery. However, in applications where the EDS-D1 unit will be installed and used in a powered aircraft, using the aircraft's electrical system becomes very desirable. The EDS-EPS, or simply EPS, is a precision voltage reducer, regulator and filtering device to operate up to four EDS-D1 or EDS-A1 units from an aircraft electrical system of 10 to 30 volts. The EPS will filter out surges, spikes and reversals caused by starter, flap, hydraulic motors and strobe lights. The EPS is a result of many of our "kit-building" customers requests. The internal battery is disconnected from the power circuit while the external power jack is plugged into the EDS-D1 unit(s).