Abstract: A safety device for an automobile battery has a light for indicating when jumper cables are properly attached to the battery, and a switch for electrically connecting a jumper cable attached to the device with a battery terminal. The device has a non-conductive housing supporting a fixed contact in electrical connection with one terminal of the battery by means of an integral clamp. A movable contact is formed by two metal plates on opposite sides of a head of the fixed contact, the plates being adapted to receive and be gripped between the jaws of a jumper cable clamp. The jumper cable clamp biases the plates toward the fixed contact. The device normally is in a non-conductive mode, in which the plates are prevented from moving together by one end of a lever disposed between the plates. The other end of the lever extends outside of the housing and has a handle. The lever is biased into the non-conductive position by a spring.

Abstract: A battery jumper-cable interconnecting system with a pair of mechanically activated high-current switches, one of which is closed to connect charged and discharged batteries in correct polarity without regard to positioning of the jumper cables. The appropriate switch to activate is determined by an automatic polarity-sensing circuit which provides a visual signal to the user by unlatching and moving the correct switch to an unlocked position, while maintaining the incorrect switch in a latched and locked position.