*Article* **Methodology for Determining Time-Dependent Lead Battery Failure Rates from Field Data**

**Rafael Conradt 1,\*, Frederic Heidinger <sup>1</sup> and Kai Peter Birke <sup>2</sup>**


**\*** Correspondence: rafael.conradt@de.bosch.com

**Abstract:** The safety requirements in vehicles continuously increase due to more automated functions using electronic components. Besides the reliability of the components themselves, a reliable power supply is crucial for a safe overall system. Different architectures for a safe power supply consider the lead battery as a backup solution for safety-critical applications. Various ageing mechanisms influence the performance of the battery and have an impact on its reliability. In order to qualify the battery with its specific failure modes for use in safety-critical applications, it is necessary to prove this reliability by failure rates. Previous investigations determine the fixed failure rates of lead batteries using data from teardown analyses to identify the battery failure modes but did not include the lifetime of these batteries examined. Alternatively, lifetime values of battery replacements in workshops without knowing the reason for failure were used to determine the overall time-dependent failure rate. This study presents a method for determining reliability models of lead batteries by investigating individual failure modes. Since batteries are subject to ageing, the analysis of lifetime values of different failure modes results in time-dependent failure rates of different magnitudes. The failure rates of the individual failure modes develop with different shapes over time, which allows their ageing behaviour to be evaluated.

**Keywords:** lead batteries; safety concept; safety battery; battery monitoring; electronic battery sensor; failure modes; failure distribution; failure rates; field battery investigation; safe supply; power supply system
