A review on the state of health estimation methods of lead-acid batteries

Batteries play an important role in modern society. Among the different types of batteries, lead-acid batteries account for over 70% of all the sales of rechargeable markets and are widely employed in people's daily lives. To avoid unexpected incidents and subsequent losses, it is considerably important to estimate the state of health (SOH) of lead-acid batteries. In this work, we review different types of SOH estimation methods for lead-acid batteries. First, we introduce the concept of the SOH and the mechanism of battery aging. Next, different SOH estimation methods are categorized into four classes: direct measurement-based, model-based, data-driven, and other methods. Then, we provide a detailed analysis of the characteristics of each method and discuss the corresponding advantages and limitations in practical applications. Subsequently, based on these characteristics, we systematically evaluate and compare different types of methods. Considering different scenarios, we indicate the recommended methods for each situation and provide the reasons for the choices. We also indicate the unsolved problems of each method to inspire further research. This review can serve as a reference for future works in this field, as no other review has been conducted on the same topic.