Cell bypassing extends the lifespan of electric vehicle batteries
Electric vehicle battery packs consist of multiple interconnected cells that age at different rates. Consequently, in conventional architectures, a cell with particularly low resistance can limit the capacity and lifespan of the entire pack.
Against this backdrop, a new study by researchers at Chalmers University of Technology examines so-called "reconfigurable" batteries. These systems use switches and control mechanisms to modify the electrical connections of individual cells or groups of cells. This allows for the selective bypassing of weaker cells, while still utilizing the remaining capacity of the pack.
In the most advanced scenario—where each cell can be controlled individually—simulations indicate that the lifespan of certain high-voltage vehicle batteries could be extended by more than 20%. According to the study, this potential is particularly significant for electric trucks and long-range electric cars, which feature a large number of cells connected in series.
Reconfigurable battery packs aim to circumvent underperforming cells.
To illustrate the magnitude of this effect, the researchers provide an example based on an 80 kWh battery with an annual mileage of 12,000 km. While a conventional battery pack might require replacement after ten years, a reconfigurable pack would reach the same level of degradation only after about eleven years—approximately fourteen months later.
Furthermore, the residual value of the pack is higher because it has aged more slowly. Although this technology requires additional electronic components—leading to higher upfront costs—the study suggests that the extended lifespan and greater residual value can offset these expenses under real-world conditions. Currently, this technology is not yet available in production vehicles. However, it is important to note that this system has been rigorously evaluated in both research and industrial prototypes, demonstrating its reliability and effectiveness. In practice, it is more likely that groups of cells will be used rather than controlling each cell individually. Therefore, the increase in service life of more than 20% represents a theoretical upper limit.
In addition to extending service life, researchers have also identified advantages in the production process. Currently, it is essential that cells with similar properties undergo rigorous compatibility testing and are carefully matched. Reconfigurable packs have the potential to tolerate greater variations between cells, which reduces the effort required for the "cell matching" process.
This architecture could offer advantages for "second-life" applications. Battery packs have the potential for an extended service life in vehicles, subsequently allowing for their reuse as stationary storage systems. This is made possible by the ability of weaker individual cells to operate independently, which reduces the need to discard the entire pack.
Chalmers is currently investigating various methods to extend the lifespan of batteries. In May, a team from the university presented an artificial intelligence-based fast-charging strategy that adapts the charging process to the battery's condition. According to simulations, this strategy should extend battery lifespan by approximately 23%. Meanwhile, the reconfigurable battery architecture—the subject of this new study—operates directly within the battery pack and is designed to selectively bypass weaker cells.
The study, titled "System-level evaluation of dynamic reconfiguration regarding the lifespan and costs of electric vehicle battery packs," has been published in the renowned journal *Nature Communications*. The project involved distinguished researchers from Chalmers University of Technology, as well as representatives from the prestigious companies PHINIA and Scania.
