In a new method, a defective electrochemical cell is detected by non-invasive means before assembly into a battery comprising multiple cells. The method detects faulty cells by sensing and detecting variations in the intensity level of infrared radiation emitted from an exterior surface of the cell or battery. The scanning and detection, preferably, is conducted by sensing infrared energy in a range of about 2 to about 12 um (microns) emitted from the major surface of the cell or battery. The variations are recorded as a function of geometric variables indicative of the geographic position of the variations.