Patent ID: 8376667

Claim:
A power tool comprising: a housing; a base coupled to a portion of the housing, the base operable for magnetically coupling the tool to a workpiece; an electric motor supported by the housing; a DC power source for providing power to the motor; an AC power input for providing power to the motor, the AC power input configured for receiving power from an AC power source; a power supply switching unit electrically coupled to the DC power source and the AC power input, the switching unit selectively electrically coupling the motor with one of the DC power source and the AC power input, wherein the switching unit includes a relay operable to switch to one of the DC power source and the AC power input upon loss of power from the other of the DC power source and the AC power input; and a power switch for providing power to the motor from one of the DC power source and the AC power input via the switching unit, wherein the DC power source includes a battery removably coupled to the housing by insertion along a plane, the plane interferingly crossing the power switch when the power switch is in an on position to thereby form an interlock between the battery and the power switch.