Generational finds cell-voltage imbalance in one in 85 used EVs tested in the UK
EV Engineering News
Posted August 28, 2026 by Chris Ruoff & filed under Newswire, The Tech.
Generational, a UK-based EV battery diagnostics company, has published an analysis of cell-level data from approximately 10,000 used-EV battery tests run through hundreds of dealers across the UK. The median vehicle showed 8 mV between its highest and lowest cell voltages, but around one in 85 tests showed an imbalance above 50 mV, and around one in 200 exceeded 100 mV.
An imbalance above 50 mV requires investigation, the company says, and at 100 mV it indicates a potential underlying fault.
An EV pack is built from several hundred cells connected in series groups. It stops charging when the first cell fills and stops discharging when the first cell empties, so one weak cell limits the whole battery, and a pack-level average won’t show it, Generational explains. The BMS may also restrict charging or discharging to protect the weakest cell, potentially affecting range, state-of-charge estimates and charging behavior. Cells drift apart and back together as the battery charges and discharges, so the company says a borderline imbalance measured at a low state of charge does not always indicate a persistent fault, while a large imbalance that survives a rebalance is materially more significant.
A headline state of health (SoH) figure measures capacity, but the company says a vehicle can display a stable SoH reading while still developing faults at cell level. In many cases, there may be no warning light, dashboard message or noticeable change in vehicle behavior until the imbalance becomes more advanced.
When a test flags a vehicle, the customer is walked through an attempted cell rebalance, then the vehicle is tested at rest to confirm whether the imbalance persists before any decision is made on further investigation, warranty support or repair.
Generational added cell-level voltage testing to its dealer diagnostics in April, and in July it partnered with Maverick Diagnostics, which serves around 6,000 UK repair shops, to bring its OBD-port test kits to those workshops.
The company’s 2025 Battery Performance Index, drawn from more than 8,000 assessments across the UK, put average SoH at 95.15% and found that variance between vehicles increases with age.
“Reporting on State of Health is essential for used EVs, but it does not tell the full story of battery condition. It measures capacity, not necessarily whether the cells inside the pack are functioning correctly,” said Oliver Phillpott, CEO of Generational. “Cell imbalance problems are often imperceptible, while the battery is developing a fault that could affect range, charging or value later on. The only practical way to see that risk early is to test for it.”
Source: Generational
Create Account. Already Registered? Log In
Virtual Conference on EV Engineering: Free to Attend
Don't miss our next Virtual Conference on September 14-17, 2026.
Register for the free webinar sessions below to reserve your spot and watch them live or on demand.
LOAD MORE SESSIONS