A safety device is wired in series with selected accessories in a wiring circuit for a vehicle. The safety device of the present invention determines the state of charge of the battery as a function of the rate of discharge of the battery. When the state of charge falls below preset values, the device...http://www.google.com/patents/US4902956?utm_source=gb-gplus-sharePatent US4902956 - Safety device to prevent excessive battery drain
