A battery low-voltage protecting device is disclosed as including an input terminal connected, via a first lead wire and a switch driver circuit, with a positive terminal of a battery; an output terminal connected, via a second lead wire, with a load; a ground terminal connected, via a third lead wire, with an automobile body and a negative terminal of the battery; a declining voltage integrating circuit; a voltage detector; and a timer switch control circuit; in which the voltage of said declining voltage integrating circuit rises when the voltage of said battery rises, and falls when the voltage of said battery falls; and the declining voltage integrating circuit can differentiate between a quick fall in the voltage of the battery from a slow fall in the voltage of the battery, and output voltage signals to the voltage detector; and the voltage sensor can receive voltage signals outputted by the declining voltage integrating circuit, to compare the voltage signals with a pre-defined voltage level, and to output voltage signals to the switch driver circuit; and the timer switch control circuit can delay the battery low-voltage protecting device from performing voltage checking by a pre-defined period of time; and the switch driver circuit can selectively open and close the connection among the declining voltage integrating circuit, the load and the positive terminal of said battery, so that when the connection among the declining voltage integrating circuit, the load and the positive terminal of said battery is disconnected, the battery is completely disconnected from all electricity-consuming appliances of the automobile.