The improved battery-powered lawnmower includes a safety key (48) that is automatically removed when the removable battery (22) is removed, while at the same time blocking the battery recharger receptacle. The lawnmower also includes a control circuit that shuts off the lawnmower upon the occurrence of one or more of several predetermined conditions, including low battery voltage, the encountering of heavy grass for a period of 3 seconds or more, and high motor current that may occur when the cutting blade is jammed. The cutting blade (264) is designed to move through any debris accumulated between the blade ends and the housing sidewall (284) without sacrificing the lift for needed cutting and mulching. The invention also includes a unique height adjustment assembly for adjusting the height of the chassis, a handle attachment that allows the handle to be positively tightened to the lawnmower chassis, and a telescoping groove (76) for the battery's quick connect/disconnect terminals.