The increasing prevalence of electrically assisted functions in vehicles makes a reliable and safe power supply from the 12V lead battery more important to meet high safety requirements. In addition to traditional battery demands – Starting, Lighting, Ignition – new performance requirements related to a ‘safe stop maneuver’ have emerged. To ensure a consistent safety approach for the vehicle and its electrical system, it is crucial to understand the reliability of the battery, including its aging and failure behavior. Previous methods for determining reliability and failure rates based on subjective teardown analyses can result in different assessments, highlighting the need for an objective method for failure determination. This study presents a nondestructive electrical test method for 12V lead batteries from car workshops and roadside assistance that identifies aging progress and dominant aging mechanisms through equation-based analysis of measured data. The battery’s ability to maintain a specified voltage threshold during an alternative load profile, the ‘safe stop maneuver’ is used to evaluate its performance for future driving applications. Teardown analyses confirmed the aging mechanisms identified during electrical testing. With a sufficiently long observation period to account for seasonal effects, this test procedure can be used to establish an objectively determined sample for further statistical reliability analyses. The results of the procedure will be published in a follow-up study.