Battery Equalization Systems: A Systematic Review of Topologies, Architectures, and Application Scenarios

Zhengqi Wei; Henry Shu-Hung Chung (IEEE Fellow)

Abstract

The large-scale deployment of electric vehicles and grid battery energy storage systems has made cell inconsistency a primary constraint restricting pack capacity utilization, cycle life, and operational safety. Most existing reviews on battery equalization focus on circuit topology analysis, placing less emphasis on architecture evaluation and unified benchmarks, which makes performance comparison and industrial scheme selection challenging. This paper presents a systematic review of battery equalization systems, structured along five interconnected dimensions: application-specific requirements, hardware topologies, energy routing architectures, standardized performance metrics, and the impact of electrochemical characteristics on equalization. Specifically, this work quantifies the diverse design requirements across transportation, grid storage, and aerospace applications, and evaluates the scalability evolution from passive to active topologies. Furthermore, this work establishes a capacity-independent benchmarking framework. This framework adopts path-dependent system efficiency and concurrent throughput as core metrics, and enables objective performance evaluation of various energy routing architectures. Ultimately, the inherent boundaries of voltage-based equalization are clarified by quantifying the correlation between open-circuit voltage versus state-of-charge (OCV-SOC) characteristics and equalization difficulty. By mapping the technological transition from isolated circuit-level optimization to macroscopic energy routing, this review establishes a definitive roadmap for engineering highly scalable and autonomous battery management systems.

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