Why we need a standardized state of health definition for electric vehicle battery packs -- a proposal for energy- and capacity-based metrics

TL;DR

This paper advocates for a standardized, energy- and capacity-based method to measure the state of health of electric vehicle batteries, emphasizing reproducibility, scalability, and deeper aging insights.

Contribution

It proposes a standardized measurement procedure for battery health assessment using onboard charging and differential voltage analysis.

Findings

Standardized method improves transparency in battery health evaluation.

Onboard charging enables reproducible and scalable assessments.

Differential voltage analysis offers deeper aging insights.

Abstract

Range and performance are key customer-relevant properties of electric vehicles. Both degrade over time due to battery aging, thus impacting business decisions throughout a vehicle's lifecycle, such as efficient utilization and asset valuation. For practical assessment, aging is often simplified into a single figure of merit - the state of health - typically defined by the battery pack's remaining capacity or energy. However, no standardized method for measuring the state of health at the vehicle level has been established, leaving both academia and industry without a clear consensus. Ultimately, standardization is crucial to increase transparency and build confidence in the long-term reliability of electric vehicles' battery packs. In this article, we propose a standard measurement procedure for assessing the capacity- and energy-based state of health, leveraging onboard charging to enable reproducibility and scalability. Additionally, we demonstrate how differential voltage analysis can provide deeper insights into battery aging at the vehicle level.