EV batteries consist of many interconnected individual cells that age at uneven rates. Manufacturing variations and daily usage cause some cells to lose capacity faster than others. Conventional battery packs connect these cells in a fixed configuration.

This fixed design forces the entire battery pack to operate at the pace of its weakest cell. The university’s researchers compare this limitation to a group of hikers tied together by a rope. The group must stop when the slowest member stops, regardless of the energy remaining among the other members.

The new architecture lets the battery management system dynamically isolate problem cells using electrical switches. Current continues flowing through the healthy cells while weak units remain bypassed. This approach extracts maximum capacity from the pack’s operational cells. Control systems activate these switches to isolate cells that limit overall performance. This hardware modification prevents weak cells from dragging down the entire system.

Changfu Zou, a professor in the Department of Electrical Engineering at Chalmers, explains that battery cell reconfigurability exists on a flexible engineering spectrum. Manufacturers decide their position on this spectrum based on cost and performance targets.  

‘Reconfiguration is not an on-or-off choice. Where a manufacturer chooses to position itself on that spectrum determines how much of the potential benefit can be realised,’ said Zou.

For example, controlling cell groups together requires less hardware but yields smaller theoretical benefits. To evaluate tangible outcomes, the university team analysed a representative passenger-car scenario. The model featured an EV equipped with an 80kWh battery pack. This vehicle travelled 12,000km annually over an expected 18.8-year lifespan. Under these specific parameters, the new battery architecture defers battery replacement by 14 months. The battery pack retains a higher residual value when removed from the vehicle and is less affected by degradation than a reference case.  

‘For a private EV owner, this could mean postponing a battery replacement. For a vehicle fleet with hundreds of battery packs, delaying that cost by a year could translate into significant savings,’ commented Albert Škegro, a PhD student at the Chalmers Department of Electrical Engineering.

However, the new architecture requires more switches, connections and advanced control systems, increasing the battery pack’s upfront cost. Within the research, the team at Chalmers analysed whether longer battery life and higher residual value can offset the additional investment.

‘The results show that the architecture can already be cost-effective under a wide range of real-world usage conditions. Based on a component-level analysis using automotive-grade hardware, the additional hardware would increase the total pack cost by approximately 9%,’ said Zou.

According to the analysis, a cost increase of around or greater than 12% would make the architecture less likely to provide an economic benefit over the vehicle’s lifetime.  

But sustainability advantages extend far beyond longer vehicle operation periods and cost reduction. Chalmers researchers report that retired EV batteries can transition into secondary applications such as stationary energy storage. Bypassing weak cells lets more of the battery pack be reused as complete units. Preserving battery integrity prevents premature material waste and avoids discarding valuable raw materials. Keeping battery packs operational longer delivers immediate environmental benefits before economic calculations begin.

Grid storage operators also evaluate reconfigurable battery modules for stationary installations. Researchers at Chalmers plan to conduct future experiments using larger battery packs under dynamic loads in addition to outdoor track testing, which will simulate aggressive driving profiles and extreme weather conditions.