Over 25k UK electric cars have battery issue that limits range and charging speed
Generational analysed the batteries of more than 1,000 EVs and while most were in a good state, some suffered voltage imbalances
Roughly one in 85 electric cars have been found to suffer from a battery cell imbalance that can affect their range and charging ability, and cost thousands to fix. With well over two million EVs on the road the issue could affect more than 25,000 UK cars.
Diagnostic data from more than 1,000 used electric cars reveals that the vast majority of second-hand EVs boast a well balanced battery, with a median of just eight millivolts (mV) between the highest and lowest voltages across its cells. However, Generational, the battery specialist that carried out these tests, says that approximately one in 85 examples have an imbalance of more than 50mV – something that could point to wider issues.
“Cell imbalance problems are often imperceptible, while the battery is developing a fault that could affect range, charging or value later on,” said Generational’s CEO, Oliver Phillpott. “The only practical way to see that risk early is to test for it.”
The London-based firm says its diagnostics tech can plug into a vehicle's On-board Diagnostics (OBD) unit and ‘interrogate’ individual cells to provide an overall picture of the battery’s State of Health. However, Generational says doing so has uncovered that as many as one in 200 cars have a serious imbalance of more than 100mV. This can not only reduce or make range more unpredictable, but it can also cause problems when charging and result in the battery management system limiting overall performance to protect the damaged cells.
A quick fix for such an issue can be a cell rebalance – charging an EV to 100 per cent via a slow AC charger and leaving it plugged-in is one way to do this – but a repair is often required. This is bad news because a battery can account for up to 40 per cent of an EV’s overall value, so repairing just a few cells can cost upwards of four figures, depending on the cell’s structure/repairability, the scale of the imbalance and whether the battery itself remains under warranty.
In fact, Generational said in one case a vehicle had an imbalance across three cells which cost “nearly £8,000” to rectify. It’s unsurprising, then, that many EVs with faulty batteries are simply written off.
Baked-in issues such as these are relatively rare and EVs are generally easier to maintain than internal combustion (ICE) cars due to having fewer moving parts. However, unlike ICE cars,where value is distributed among a variety of elements such as the engine, gearbox and so on, an EV’s battery and the systems that manage it can be worth more than the rest of the vehicle. Plus, although a faulty petrol car can be identified by dubious sounds or smells, for example, signs of a fault in an EV are not always visible, which strengthens the case for battery passports and State of Health checks.
From February 2027, when an electric car is sold, it must be accompanied by a digital ‘passport’ (accessed by a QR code) that contains information on the carbon footprint, materials, recyclability and State of Health of its batteries. This is designed to give consumers greater insight and confidence – particularly on the used market.
However, not all battery State of Health checks are the same – Generational’s approach, for example, reveals problems such as cell imbalances that aren’t necessarily picked up elsewhere – which is why experts from across the industry are calling for more standardisation. In one case, a paper published by various German universities proposed “a standard measurement procedure for assessing the capacity and energy-based state of health, leveraging onboard charging to enable reproducibility and scalability”.
In the meantime, transport research organisation, New Automotive, has called for mandatory battery health checks in the UK to support second-hand EV sales. “The next stage of Britain's transition to electric vehicles will be driven by the used market. Every new EV sold today becomes tomorrow's affordable family car,” said chief executive Ben Nelmes.
“Government policy has done a good job of creating supply, but the challenge now is stimulating demand,” he said. “Battery health certificates are a practical, proportionate reform that would strengthen consumer confidence without requiring expensive subsidy schemes.”
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