They analyze 10,000 used electric cars and uncover the truth about their batteries

This has for years been one of the most repeated arguments against electric cars—that the battery needs to be replaced after five years and that we’ll have to sell a kidney to afford it. The data show something completely different.

The British company Generational, specialized in battery diagnostics, has published the results of an analysis conducted on approximately 10,000 used electric cars. Its goal was to check the voltage balance among the different cells that make up the batteries and detect any potential anomalies that could indicate future problems.

The results are quite reassuring. According to the data collected, only one in every 85 cars analyzed showed voltage differences high enough to warrant a more thorough inspection. And this doesn’t necessarily mean those batteries were faulty, but rather that their readings required further investigation.

To understand the significance of these results, it’s important to remember that a battery consists of numerous cells arranged in different configurations. All of them must work together in coordination, maintaining relatively balanced voltages so that the entire system functions properly.

In the cars tested, the typical difference between the cell or group of cells with the highest voltage and those with the lowest voltage was only about 8 millivolts (mV). This is a very small figure that, according to Generational, indicates that the vast majority of batteries maintain good internal balance.

Differences exceeding 50 millivolts occurred in approximately 1.18% of the cars analyzed. Experts consider this value high enough to warrant further checks, although it alone does not indicate a fault.

Even more interesting are the results related to the most significant deviations. Differences above 100 millivolts, which could signal an internal problem, appeared in just one out of every 200 electric cars, roughly 0.5% of the sample.

This means that out of the 10,000 cars tested, around 50 had a voltage difference exceeding that threshold. It’s important to emphasize that we’re talking about potential anomalies, not 50 confirmed defective batteries.

A battery may appear healthy while hiding a problematic cell

One of the most interesting aspects of this study is that it highlights the limitations of one of the most commonly used indicators for assessing second-hand batteries: health status, known by its acronym SoH.

This percentage indicates how much capacity a battery retains compared to when it was new. For example, if a battery originally had 60 kWh of usable capacity and can now store 54 kWh, its health status would be approximately 90%.

However, a battery with good health status is not necessarily free of internal problems. It may retain high capacity while still having one or more cells that behave differently from the rest.

This is important because the battery management system continuously monitors the voltages and temperatures of its components. If a cell reaches its maximum limit during charging or its minimum limit during discharging before the others, the system must intervene to protect the entire battery.

In certain circumstances, a single problematic cell can end up affecting the performance of the entire battery, reducing its available range, altering its behavior during charging, or causing inaccurate readings of the remaining charge percentage.

However, there’s no need to panic if voltage differences occur. Generational reminds that these may be related to the charge level, previous use of the vehicle, or temporary imbalance among the cells.

Therefore, before discussing repairs, experts recommend repeating the measurements under proper conditions and checking whether the issue can be resolved through a balancing process. In some cases, this may be sufficient to restore normal operation without the need to replace components.

The results also align with another previous study by the same company, which analyzed over 8,000 battery inspections and found an average health status of 95.15%.

Even among electric cars that are eight or nine years old, the median retained capacity was around 85%. In other words, half of the cars in that group maintained at least that percentage of their original capacity.

These figures help dispel the notion that electric car batteries degrade rapidly and become an economic burden for owners after a few years.

The conclusion is that for those considering buying a used electric car, the recommendation remains to conduct an independent diagnosis before finalizing the purchase. It’s not enough to consider only the age, mileage, or even the battery’s health percentage. It’s also important to check how the battery cells perform and whether there are any abnormal differences between them.

The good news is that, according to Generational’s data, finding a battery with significant abnormalities is much less common than many buyers assume. And given the savings that buying a used electric car can offer compared to a new one, having this information available can help make a decision with much greater confidence.