A joint research effort by a team led by Chen Zhongwei at the Dalian Institute of Chemical Physics under the Chinese Academy of Sciences and a group led by Zou Changfu at Chalmers University of Technology in Sweden has produced new findings on why electric vehicle battery packs often retire earlier than expected. The study was released on September 10, 2026, and draws on more than three years of real-world operational data.
The researchers analyzed hundreds of vehicles equipped with two major battery chemistries: nickel-cobalt-manganese (NCM) ternary lithium batteries used in passenger cars, and lithium iron phosphate (LFP) batteries used in city buses. Their central discovery is what they term the “weakest cell” effect. Because individual cells within a pack age at different rates, the single most degraded cell can reach its end-of-life threshold well before the rest of the pack, and once that happens, the entire battery pack is forced out of service—even though the majority of its cells may still have usable capacity remaining.
The impact of this effect is substantial. According to the study, the weakest-cell phenomenon shortens the service life of passenger car battery packs by 17.7 percent, while their energy utilization rate drops to just 80.7 percent. For buses equipped with LFP batteries, the consequences are even more pronounced: pack lifespan is reduced by 22.8 percent, and energy utilization falls to 72.9 percent.
These figures highlight a significant but often overlooked inefficiency in current battery system design. Rather than failing gradually across all cells, packs are effectively retired by their single worst-performing cell, leaving considerable potential capacity unused.
To address the problem, the research team proposes a combination of strategies. Improving manufacturing consistency would reduce the initial variation among cells, slowing the divergence in aging rates. Better thermal management could help keep cells within a more uniform temperature range, since temperature differences are a key driver of uneven degradation. Additionally, the team suggests adopting reconfigurable pack designs that would allow the system to bypass or isolate the weakest cells, enabling the remaining healthy cells to continue operating and extending the overall useful life of the battery pack.
The findings carry practical implications for both automakers and fleet operators, particularly as the world pushes toward broader EV adoption and seeks to maximize the value and sustainability of every battery pack produced.
