The invention relates to the field of anti-theft technology, in particular to a battery car anti-theft alarm device and a method, wherein the method comprises a power supply is connected, a relay works, and a normally closed contact is in an off state, when motor car signals are sent, a horn of a car alarm sounds, a build-in horn of the car alarm also can sound, and a light emitting diode flashes to alarm. A charging plug is pulled up from an A position (such as a three-core coaxial line), a charging loop is cut off, break-over voltage on the two ends of the light emitting diode disappears, the light emitting diode changes into a non-conducting state from a conducting state, work current loops on the two ends of a relay coil are cut off, the normally closed contact returns to a closed state, and an audible and visual alarm works. The battery car anti-theft alarm device uses wired protection, uses cables to transport signals, alarms through sound and light, double warms on vision and auditory, and is intuitive and clear. A 36V-48V low voltage direct current power supply which is changed from a 220V alternating current power supply leads to the front of an electric car, thereby eliminating hidden trouble of leakage. The battery car anti-theft alarm device and the method use special circuit design, thereby leading motor cars to obtain multi-azimuth protection.