Europe redefines the battery for electric buses

Funded by the European Union under the Horizon Europe program and led by France’s CEA, SIERRA brings together 11 partners from 7 countries with a clear objective: to create an energy storage system optimized for the real demands of heavy-duty transport. This is not about adapting automotive batteries, but about designing them from the ground up for bus operations.

The project focuses on high-nickel NMC chemistry, aiming to increase energy density without compromising safety or lifespan. In the bus segment, this is critical: these vehicles operate under intensive duty cycles, with frequent charging and discharging, high thermal loads, and the need for absolute reliability.

But SIERRA goes beyond the cell itself. The development covers the entire battery pack: lighter structures through multi-material enclosures, advanced monitoring systems for state of charge and health, optimized thermal management, and the use of digital twins to validate real-world performance.

The goal is to reach TRL6, meaning the technology will be validated in a relevant environment and brought closer to industrial deployment.

In a market where Asia clearly leads battery technology, SIERRA represents a strategic move by Europe to close the gap. And it does so with a strong premise: the future of electric buses depends not just on more energy, but on the right energy—designed to meet the real demands of public transport.