Cell bypass is intended to extend the usability of electric car batteries.

A study by Chalmers University of Technology explores reconfigurable battery packs that can selectively bypass weaker cells. Under optimal conditions, this could extend the lifespan of batteries in certain high-voltage vehicles by more than 20 percent.

Image: Chalmers University of Technology | Albert Skegro

The battery packs in electric vehicles consist of numerous interconnected cells that do not age at the same rate. In conventional architectures, a particularly weak cell can therefore limit the usable capacity and lifespan of the entire pack.

This is exactly where a new study by researchers from Chalmers University of Technology in Gothenburg begins. The study focused on so-called reconfigurable battery packs, in which switches and control systems can alter the wiring of individual cells or groups of cells. Weaker cells can be bypassed selectively in this way, while the remaining capacity continues to be utilized.

In the most advanced case, where each cell can be controlled individually, model calculations show that the lifespan of certain high-voltage vehicles could increase by more than 20 percent. According to the study, the potential is especially significant for electric trucks and long-range electric cars with many cells connected in series.

Reconfigurable battery packs aim to bypass weak cells

The researchers illustrate how significant the effect can be using an example with an 80-kWh battery and an annual driving distance of 12,000 kilometers. If a conventional battery pack is replaced after ten years, the reconfigurable pack reaches the same level of degradation in the model only after about eleven years, or roughly 14 months later.

In addition, there is a higher residual value because the pack has aged less. Although the technology requires additional electronics and thus incurs higher initial costs, the study suggests that longer lifespan and higher residual value can offset these extra expenses under realistic conditions.

In production vehicles, this technology is not yet available. However, it has already been tested in research and industrial prototypes. In practice, cell groups are likely to be used rather than individual control of each cell. The more than 20 percent longer lifespan represents a theoretical upper limit in this regard.

In addition to lifespan, researchers also see advantages in production. Currently, cells with as similar properties as possible must be thoroughly tested and combined together. Reconfigurable packs could tolerate greater differences between cells, thereby reducing the effort required in what is known as cell matching.

The architecture could also offer advantages for Second-Life applications. Battery packs could remain installed in vehicles longer and then be reused more effectively than stationary storage, as individual weaker cells do not necessarily force the entire pack out of service.

The Swedish university is already researching several approaches to extend battery life. In May, a team from the institution introduced an AI-driven fast charging strategy that adjusts the charging process to the battery’s condition, aiming to extend its lifespan by about 23 percent in the model. The reconfigurable battery architecture being studied now addresses the issue at the battery pack level itself, aiming to bypass weaker cells specifically.

The study titled “System-level assessment of dynamic reconfiguration for lifetime and cost outcomes in electric vehicle battery packs” was published on nature.com. Researchers from Chalmers University of Technology, along with representatives from PHINIA and Scania, were involved in it.