The present invention provides a device for automatic detection of battery polarity, wherein a detector circuit is structured from detector terminals, detector units, positive voltage electrical connecting units and negative voltage electrical connecting units. Operational procedure involves first connecting battery electrical conducting units with the detector terminals of the detector circuit, when the detector terminals are connected to positive poles of the battery, then one set or more than one set of the detector units of the detector circuit detect positive voltage, which actuate an electrical connection with the positive voltage electrical connecting units, thus connecting positive poles of the detector device to the detector terminals and connecting to positive poles of the battery, at the same one set or more than one set of the detector units determine negative voltage and actuate a connection with the negative voltage electrical connecting units, thereby forming a complete circuit.