On August 18, 2015, about 0900 mountain daylight time, a Schweizer 269C helicopter, N17YS, experienced a complete loss of engine power and subsequent hard landing about 10 miles northwest of the North Las Vegas Airport (VGT), Las Vegas, Nevada. The certified flight instructor was not injured, and the pilot undergoing instruction sustained minor injuries. The helicopter sustained substantial damage to the tailboom. The helicopter was privately owned and operated by Airworks Aviation Academy under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed and no flight plan was filed for the local flight. The flight originated from VGT at 0845. The flight instructor reported that after the student leveled the helicopter off at 4,500 ft mean sea level, he was going to demonstrate, with the student following along on the controls, entry procedures for an autorotation maneuver. The flight instructor smoothly lowered the collective, input right pedal, and pulled back on the cyclic to enter the autorotation. Immediately after entering the maneuver, he heard a change in engine noise and he observed that the engine RPM gauge was zero. The flight instructor attempted several times to restart the engine by pressing the start button, however every time the start button was pressed, there was no indication that the starter engaged. The flight instructor continued the descent to the ground. The helicopter landed hard; subsequently, the main rotor blades severed the tailboom. A postaccident engine examination conducted by a Federal Aviation Administration Inspector revealed that the positive lead was found separated from the battery terminal, and that the lead exhibited corrosion. The positive lead was attached to the battery, and the engine started and operated normally.