Why balancing is essential for every traction battery

AVILOO explains why balancing cell voltages is crucial for range, performance, and safety in modern electric vehicles.

Balancing is one of the most important - yet least visible - processes in electromobility. Without this system‑critical function, the range, safety, and service life of an electric vehicle would decrease significantly. The independent battery diagnostics specialist AVILOO explains why balancing is indispensable and how the Battery Management System (BMS) uses it to ensure optimal traction battery performance.

 

 

What happens inside a traction battery?

A modern EV battery consists of hundreds to thousands of individual cells connected in a way that provides high voltages (300–800 volts) and enough capacity to deliver long driving ranges. Patrick Schabus, Chief Product Officer at AVILOO, illustrates a typical setup: “Three cells are connected in parallel to form one cell block. A total of 108 of these blocks are connected in series—resulting in 324 cells overall.” While cells connected in parallel automatically equalize their state of charge, this does not happen in series connections. And that is where balancing becomes essential.

 

Why is balancing so important?

Balancing aligns the State of Charge (SoC) across all cell levels. Without this equalization, even the smallest variations can grow significantly over time. These variations may be caused by:

• Production tolerances
• Temperature differences
• Uneven load distribution
• Natural aging

Even small deviations mean that some cells become full or empty earlier than others. Because the weakest cell always determines the usable energy of the entire pack, imbalances can lead to major issues:

• Reduced range
• Inaccurate SoC readings – drivers may overestimate their remaining range
• Accelerated battery aging
• Increased risk of cell defects, potentially raising the fire risk

In short: without balancing, a traction battery cannot remain safe or durable.

How does balancing work?

In the EV industry, top balancing is the standard. At the end of the charging process, SoC differences are corrected so that:

• range predictions remain accurate
• the battery’s full energy is accessible
• cell lifetime is maximized

 

How the balancing process works in detail:

At 100% SoC, the BMS determines the required balancing capacity for each cell level. Each unit is discharged via a balancing circuit until all cell levels reach an equal state. This process can also occur during vehicle operation. The more complex the battery architecture, the more important balancing becomes. 800‑volt systems, for example, have twice as many cells in series as 400‑volt systems—and therefore rely even more on precise balancing.

 

Balancing and State of Health (SoH): How AVILOO enables accurate diagnostics

Balancing not only ensures optimal performance—it is also a key indicator of a battery's State of Health. The BMS measures critical parameters such as:

• Capacity loss
• Internal resistance
• Charging behavior

AVILOO combines these data points with the FLASH Test, which provides a comprehensive battery analysis in just three minutes. The test evaluates:

• cell voltages
• SoC deviations
• results visualized in a heat map, ranging from green (optimal) to red (critical)

 

The right SoC level is crucial for accurate diagnostics:

For NMC/NCA batteries, reliable evaluation is possible from 80% SoC. For LFP batteries, from 95% SoC.

 

Conclusion: Balancing Is Essential for Range, Longevity, and Safety

Without effective balancing, a modern traction battery would be barely functional. Balancing protects the cells, preserves range, and reduces the risk of severe cell defects. Patrick Schabus summarizes it clearly: “For the driver, good balancing means more range, longer battery life, and maximum safety.”

 

Recommendation for EV drivers

To reliably assess the health of a traction battery, EV drivers should periodically perform an AVILOO FLASH Test at 100% SoC. This allows potential risks to be detected and mitigated early.