Cell bypass aims to extend the usable life of EV batteries

A study by Chalmers University of Technology examines 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 per cent.

Image: Chalmers University of Technology | Albert Skegro

Battery packs in EVs 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 precisely where a new study by researchers from Chalmers University of Technology comes in. It examines so-called reconfigurable battery packs, in which switches and control systems can alter the wiring of individual cells or cell groups. Weaker cells can thus be selectively bypassed while the remaining capacity continues to be used.

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

Reconfigurable battery packs aim to bypass weak cells

To illustrate the scale of the effect, the researchers use an example with an 80-kWh battery and an annual mileage of 12,000 km. If a conventional battery pack is replaced after ten years, the reconfigurable pack reaches the same ageing state in the model only after around eleven years – about 14 months later.

Additionally, the residual value is higher because the pack has aged less. Although the technology requires additional electronics and thus incurs higher initial costs, the study suggests that the longer service life and higher residual value can offset these additional costs under realistic conditions.

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

Beyond extending lifespan, the researchers also see advantages in production. Today, cells with the most similar properties must be extensively tested and matched. Reconfigurable packs could tolerate greater differences between cells, thereby reducing the effort required for so-called cell matching.

The architecture could also offer benefits for second-life applications. Battery packs could remain in use in vehicles for longer and subsequently be better repurposed as stationary storage systems, as individual weaker cells would not necessarily force the entire pack out of operation.

Chalmers is already researching several approaches to extend battery life. In May, a team from the university presented an AI-based fast-charging strategy that adapts the charging process to the battery’s condition and is expected to extend its lifespan by around 23 per cent in simulations. The newly studied reconfigurable battery architecture, on the other hand, works directly within the battery pack and is designed to selectively bypass weaker cells.

The study, titled “System-level assessment of dynamic reconfiguration for lifetime and cost outcomes in electric vehicle battery packs,” has been published in the journal _Nature Communications_. Researchers from Chalmers University of Technology, as well as representatives from PHINIA and Scania, were involved.