State of Charge Degradation of AGM Starter Batteries in Automotive Power Nets

The aim of this paper is to explore the changes of state of charge (SoC) distributions, due to the aging of batteries in vehicle fleets. For this purpose, the state of charge distribution of a new vehicle is modified in order to represent a vehicle with a sulfated battery. This new distribution is then combined with the probability distribution of the level of sulfation to create the SoC distribution of the aged fleet. The resulting SoC distributions for aged fleets match the corresponding measured distributions.To model the probability of the sulfation level in the battery, the paper analyzes 171 batteries and presents Weibull distributions to describe the probability for this aging behavior. These distributions exhibit a high accuracy within 4 different time ranges and their parameters have a linear time dependent behavior.