Unbalanced EV battery packs can have a massive impact on your vehicles’ performance, efficiency and reliability. If just one cell lags behind, the whole pack suffers. This unbalancing is a natural part of a battery’s lifespan, and thankfully, the vehicle’s computers automatically correct it, thanks to battery balancing when your EV has almost finished charging.
On this page, we’ll walk you through why imbalance matters and how to navigate this hurdle. And we’ll talk about the concept of inductive balancing and how the vehicles of the near future could bring your fleet its fantastic benefits.
Why imbalance costs you
Like most EVs, battery-powered fleet vehicles rely on packs made up of many lithium-ion cells, usually wired in series. Over time, slight differences in resistance or capacity cause some cells to charge faster than others, resulting in a voltage imbalance that needs manual correction.
Your EVs have onboard systems ready to handle this. In most models, this is known as passive balancing, which deals with this voltage imbalance by burning off excess charge as heat. That means cells don’t overcharge, which would cause chemical instability and potentially lead to thermal runaway.
Passive balancing is straightforward, but wasteful. It burns off excess charge as heat, draining energy you’ve already paid to store. That means reduced range, shorter battery life and lower pack efficiency, even though you’re still pulling power from the grid to top up every cell, whether the cells need it or not.
One possible solution, currently in R&D, is inductive balancing, a form of active balancing (as opposed to ‘passive’ balancing). Like other balancing methods, it would be built into the vehicle’s onboard battery management system (BMS). It’s not in mainstream production anywhere yet, but here’s why it matters all the same.
How inductive balancing might actually work
Inductive balancing will be an integrated process within the BMS. It’s another approach to addressing the natural battery imbalance issue. In short, instead of ‘burning off’ extra charge, it moves the charge from higher-voltage cells to lower-voltage ones. Tests show inductive methods can transfer energy between cells with over 99% efficiency, and it usually takes only a few minutes. That makes it ideal for high-demand fleets or fast-charging cycles where downtime and thermal stress need to be avoided.
Inductive balancing will use coils and switches to store and transfer energy. While there are several ways this can be done, the most common approaches so far are known as cell-to-cell, coupled inductor, and cell-to-pack.
- Cell-to-cell systems transfer energy directly between two individual cells using switches and an inductor or capacitor. Efficient and fast, but requires complex control circuitry to manage multiple cell pairs.
- Coupled inductor systems use one or more inductors with magnetically linked windings to transfer energy between multiple cells. Compact and efficient, this design can balance several cells with fewer components, ideal for scalable systems.
- Cell-to-pack systems move excess energy from a high-voltage cell back into the entire battery pack (often via a shared bus), where it redistributes naturally. Simpler wiring, but less precise than cell-to-cell balancing.
Most hypothetical and test systems use pulse-width modulation (PWM) to control the amount of current flowing through the inductor. Algorithms monitor voltage or estimated state of charge (SoC), then decide which cells need energy moved in or out. The best systems adjust in real time as the pack charges or discharges.
The key benefits compared to passive balancing are less energy waste, less heat, and faster balancing.
But, as mentioned, there’s a catch. At the time of writing, although inductive balancing is being explored in more detail, almost all passenger EVs still use passive balancing. There are a few and far between exceptions, but they’re found in hybrid hypercars and concept vehicles, things you’re unlikely to have in your fleet.
Why fleet technicians should start taking notes
Yes, inductive battery balancing isn’t yet mainstream. But it could be soon. The global market for active cell balancing is growing fast, from $2.1bn in 2024 to a projected $5.9bn by 2032.
The issue with battery imbalance is that, if you aren’t looking for it, problems appear out of nowhere. Those microscopic differences in cells that occur when they leave the production line slowly worsen over time, thanks to fast charging, heavy loads and regenerative braking, in short, due to general use and wear and tear. Active balancing should make all these problems much rarer.
But until such a time as inductive battery balancing becomes popular, what should you do?
Well, Rotronics is here to help. We’re helping support fleet workshops and garages all around the UK with our EV battery testers that help diagnose imbalance early, far before any noticeable symptoms emerge. The Midtronics xMB‑9640 is a high-powered module balancer that safely equalises charge across EV and hybrid battery modules up to 96v (20a). With built-in diagnostics, Wi‑Fi connectivity and intuitive controls, it’s the go-to tool for modern workshops servicing and balancing high-voltage vehicle systems. Until inductive battery balancing becomes mainstream, this remains the best way to monitor your fleet’s battery health.
Get in touch with our friendly team today to learn more and see how all these incredible benefits cost less than you might imagine.
