Battery health for used plug-in hybrids (PHEVs) shows greater variation than for used battery electric vehicles (BEVs), a new study has revealed.
PHEVs have a wider spread of battery state of health, despite broadly similar average battery performance
Analysis of 2,000 used vehicles from dealers found that PHEVs have a wider spread of battery state of health (SoH), despite broadly similar average battery performance.
The study, spanning 1,000 PHEVs and 1,000 BEVs of comparable age and mileage, found that both sets retained strong average battery health. PHEVs averaged 94.27% SoH, compared with 94.94% for BEVs.
But variation was “materially greater” among PHEVs, with 5.48% SoH standard deviation versus 4.14% for BEVs.
Generational said the wider PHEV spread suggests that battery performance may be more heavily shaped by differing usage profiles, charging behaviour and driving patterns than those seen in BEVs.
The battery health testing experts also found that 4.70% of PHEVs in the sample had an SoH below 85%, compared with 1.50% of BEVs. While the proportion of lower-performing vehicles remains small across both groups, PHEVs were more than twice as likely to fall below that threshold within this dataset.
The findings point to a notable difference in how PHEVs and BEVs are used in the real world. BEVs are generally dependent on the battery as the vehicle’s primary energy source, meaning owners and operators typically develop more consistent charging and usage routines.
PHEVs, by contrast, can be used in a wider range of ways; some are charged frequently and driven largely on electric power, while others may rely more heavily on the combustion engine, or may experience shallower, more frequent charge and discharge cycles.
As a result, two PHEVs of similar age and mileage may have very different battery histories.
Generational said this makes verified battery testing an essential part of the decision-making process for dealers, remarketers, financiers and buyers seeking to understand the true condition of a used plug-in vehicle.
Generational said the data reinforces how battery condition needs to be assessed on a case-by-case basis
The firm’s chief executive Oliver Phillpott said the spread of results among PHEVs underscores how both buyer and seller need to double down on checking the usage profile of the vehicle in question.
“Even while the averages are reassuring, for both parties the data reinforces how battery condition is something that needs to be assessed on a case-by-case basis. Transparent testing allows strong vehicles to be priced confidently and problematic vehicles to be identified early. So, across both segments, retailers and consumers can go into the market confident of finding a robust vehicle to meet their needs.”
The new PHEV versus BEV analysis follows the publication of Generational’s 2025 Battery Performance Index. Based on more than 8,000 battery health assessments conducted in 2025, the Generational’s 2025 Battery Performance Index, with even eight- to nine-year-old vehicles retaining around 85% median capacity, comfortably above common OEM warranty thresholds.
The analysis also found that high-mileage EVs with 100,000+ miles frequently returned 88-95% SoH, challenging the assumption that mileage alone is a reliable predictor of battery condition.
The Battery Performance Index concluded that battery degradation is not the systemic risk it is often assumed to be, but that variance between individual vehicles becomes more important as vehicles age.
It also argued that uncertainty, rather than underlying battery longevity, is now one of the principal constraints on used EV confidence, residual values and transaction efficiency.
Phillpott said that as the used EV and PHEV market enters a rapid growth phase, buyers need clear, trusted information before they can buy with confidence.
“Our latest analysis shows why a single mileage or age figure cannot tell the whole story. Battery condition is becoming the defining factor in used plug-in vehicle value, and the industry now has the data and tools to make that condition visible.”
Generational’s recently published Battery Performance Index can be downloaded here.