*3.2. Failure Modes of Lead Batteries*

Various ageing effects influence the performance of batteries and contribute to battery failure. Ruetschi investigates the ageing mechanisms of lead batteries in [22], where more detailed explanations of the failure modes mentioned in this section can also be found. Brik et al. presented their causal relation structured in a fault tree in [23]. However, the focus of this work is on the statistical consideration and the principle development of the different failure modes. The field data with the failure modes presented by BCI in [13] are only used to show the methodology. For safety applications, higher requirements apply for the design of a safety concept. This also includes the 12 V battery as a safe power supply. Therefore, suitable monitoring with energy management is a premise for safe operation of the battery. However, this cannot be assumed for the BCI sample, and hence this sample only serves to demonstrate the methodology. In addition to very old batteries, this sample includes various technologies that were operated with different load scenarios, that cannot be derived from the published data. However, the operation was rarely done with a suitable energy management. Moreover, the failure criterion used for this sample is the ability to start the vehicle. Nevertheless, this database is used to demonstrate the methodology and for this purpose the failure modes are described again in this section. These failure modes summarise different battery ageing mechanisms and can thus be categorised as sudden faults and gradual faults. The sudden faults occur abruptly and without notice and thus cannot be detected or predicted by diagnostic functions with a battery sensor. The sudden faults lead to a complete loss of power. The gradual faults refer to battery failures caused by ageing mechanisms and wearing out that occurs slowly during use and can thus be detected by appropriate diagnostic functions [10,24].
