A hand-held knockout driver includes a main housing having a handle portion, a motor positioned within the main housing, a hydraulic assembly driven by the motor and including a reservoir containing hydraulic fluid, a secondary housing coupled to the main housing and defining a bore therein, a working piston moveable within the bore between a rest position and an actuated position, and a work zone defined between the secondary housing and the working piston into which pressurized hydraulic fluid discharged from the hydraulic assembly is received. One unit of fluid is added to the work zone to move the working piston from the rest position to the actuated position. The reservoir has a fill capacity no greater than about 1.5 units of fluid.