The EY78A1 was part of Panasonic’s professional “Tough Tool” series, using a 15.6V (4-cell Li-ion) battery system (EY9201, EY9205, etc.). It is notable for a metal gearbox housing, high torque, and a ratcheting 1/4" hex quick-connect chuck (not a standard keyless drill chuck). It was primarily a driver/drill for screws and light drilling, not a hammer drill.