Techno-Economic Comparison of State-of-Charge and State-of-Health Balancing in Second-Life Modular Battery Energy Storage Systems

Modular battery energy storage systems (MBESSs) are a suitable solution for the integration of second-life batteries (SLBs), which show great promise to reduce the cost of gridscale energy storage. There are two common MBESS control methods, viz., state-of-charge (SoC) balancing and state-of-health (SoH) balancing. Under SoC balancing methods different SLBs reach their end-of-second-life (EoSL) separately. Alternatively, SLBs reach EoSL together under SoH balancing methods, thus reducing maintenance costs. However, SoH balancing accelerates the overall degradation of the MBESS, which reduces the profit of SL-MBESSs and presents a trade-off with the reduced maintenance costs. Unfortunately, weighting this trade-off is complicated due to the uncertain SoH and costs of SLBs. In light of this, this paper presents a techno-economic comparison to determine whether SoC balancing or SoH balancing methods are more profitable for SL-MBESS. Particularly, a survey is presented to elucidate the expected range of SoH disparity in SLBs. Accordingly, Monte-Carlo simulations are carried out to determine which method yields lower costs under different SLB disparity and price scenarios. © 2025 IEEE.