Used Car Battery Health Explained

The Charge of the Second Hand: Navigating the Battery Puzzle in Used Electric Cars

A couple discovered a 2021 model of the Nissan Leaf with only 29,000 miles on the clock. After the dealer confirmed the battery's vitality—a measure called State of Health (SOH)—was still around 93 percent, they were convinced. For a price of £12,500, they acquired the vehicle, which was a practical option for their requirements, providing a large boot and sufficient passenger room.

The purchase represented a significant shift in the pre-owned automobile market. Traditionally, buyers focused their attention on a vehicle's age and the distance it had travelled. These two figures told the most important parts of a car's story. Now, as the country transitions towards electric mobility, a new and arguably more vital statistic has emerged. How healthy a battery is has become the new headline detail for any potential owner of a previously owned electric car.

A New Kind of Forecourt Concern

The cabinetmaker who bought the Leaf also possesses a more stylish electric SUV made by Volvo. He finds the Leaf a bit underwhelming, preferring cars with a sportier feel. Despite his lack of enthusiasm for its style, he confirms the vehicle has functioned precisely as anticipated throughout the first three months since its purchase. His experience highlights a growing consumer reality where function often trumps form in the affordable EV segment.

This new reality brings with it a fresh set of anxieties. Potential buyers now grapple with questions the last generation of motorists never had to consider. How did the previous owner treat the battery? Did they frequently use rapid chargers to fill it to 100 percent capacity? This behaviour can accelerate the degradation of a battery's cells, potentially shortening its effective lifespan and reducing the car's maximum range. This uncertainty has understandably made some consumers hesitant to invest.

The Battery Black Box Problem

The history of a used electric car's power source can feel like a complete mystery. This information gap, a dilemma concerning the battery's unknown past, has created a barrier for many people thinking about making the switch to electric. Without a clear picture of the battery's past, a purchase can feel like a significant gamble. However, a new industry is rising to meet this challenge.

Firms specializing in battery analytics assert they can unlock the secrets held within these power units. They offer services that provide a highly accurate assessment of a pre-owned EV battery's state. Their detailed reports are helping to demystify the process for consumers. Furthermore, many industry experts now observe that some electric vehicle batteries are demonstrating far greater longevity than was widely predicted just a few years ago, adding a layer of confidence to the market.

Understanding State of Health

A metric known as State of Health, or SOH, is the primary way to evaluate an EV's battery. It represents the battery's current maximum capacity as a percentage of its original capacity when it was new. A battery with a 90 percent SOH can hold 90 percent of the energy it could when it first left the factory. This figure directly impacts the vehicle's potential driving distance.

However, the SOH figure displayed on a car's dashboard is not always the full story. Manufacturers use different algorithms to calculate this percentage, and the results can sometimes be optimistic or lack detail. This is where independent analysis becomes so valuable. It offers a transparent and unbiased evaluation, giving a prospective buyer a much clearer understanding of the asset they are considering purchasing.

The Tale of the Air-Cooled Battery

The Nissan Leaf provides a compelling case study in battery technology. Early generations of this popular electric vehicle were built without a sophisticated liquid-based cooling system for their power packs. Instead, they relied on air cooling, which is less effective at managing the high temperatures that can occur during rapid charging and in hot climates. Nissan has since corrected this in its latest models.

Information reviewed by NimbleFins, a US research firm, shows that these earlier Leaf models can exhibit a more considerable year-on-year reduction in their driving range compared to competitors with active thermal management. Despite this known issue, many owners, like the cabinetmaker Mr Dunstan, remain untroubled. He charges his EVs to 100 percent whenever he needs to, focusing on convenience rather than adhering to battery preservation strategies.

Independent Auditors Offer Clarity

For buyers troubled by concerns about battery longevity, several companies now offer a solution. Aviloo, a firm based in Austria, for example, provides detailed certificates verifying battery condition. Patrick Schabus, who holds the role of chief product officer at the company, affirms that they can determine a battery's vitality with complete independence and accuracy. The market includes a growing number of specialized businesses, and Aviloo is among them.

For prominent UK companies such as British Car Auctions, Aviloo supplies battery health assessments. It offers customers two main products. One option is a premium assessment, during which EV owners attach a small data-logging box to their car. The device monitors the battery's performance over several days as the owner drives the car until the battery is depleted to a 10 percent level, gathering comprehensive real-world data.

Rapid Testing for Quick Results

Alternatively, customers can choose a more rapid flash assessment. This method employs a separate diagnostic box to extract information directly from the vehicle's own battery management system. This data is then interpreted using a proprietary computer model to generate a health report. Mr Schabus noted that this entire procedure can be completed with the car stationary in less than two minutes, offering a convenient option for dealerships and private sellers.

The premium assessment provides a much deeper level of insight. It carefully watches the battery's discharge pattern, detecting any subtle shifts in voltage or current. According to Aviloo, this detailed observation can yield highly specific data on the state of each individual cell inside the main battery pack. This granular data can be invaluable in identifying potential issues before they become major problems.

Challenging Conventional Wisdom

Marcus Berger, the chief executive of Aviloo, mentioned that his organization's analytical findings sometimes show a substantial divergence from the SOH percentages provided by the internal diagnostic systems of some vehicles. This highlights the potential for inbuilt diagnostics to provide a less than complete picture of a battery's true condition. He also challenges the conventional wisdom surrounding battery lifespan.

It is a common belief in the industry that a battery with an SOH under 80 percent is too degraded for further use in a vehicle. Mr Berger argues this is not always the case. He contended that an EV with a health status below that benchmark can remain an excellent vehicle for the right person, particularly for those who primarily undertake shorter journeys. The key, he insists, is that the vehicle must be valued appropriately to reflect its reduced range.

Real-World Owner Experiences

Lucy Hawcroft, a New Zealand-based EV driver with a job in sustainability at an infrastructure firm, purchased a Nissan Leaf with her husband approximately three years back. She was an early adopter of the technology. She remembered receiving a state of health figure of about 95 percent from the selling dealer. About twelve months after the purchase, however, they had an unaffiliated mechanic evaluate the SOH once more.

The result showed a significant drop. She recalls her husband feeling surprised and a little concerned by the rate of degradation. Despite this, the vehicle continues to meet their daily needs. On a full charge, it delivers a dependable range of about 160 kilometres (100 miles), which is more than enough for their typical brief trips that are 10 kilometres or less. The experience demonstrates how battery health is relative to a driver's individual use case.

Building Trust Through Transparency

For David Smith of Cleevely Electric Vehicles in Cheltenham, where he is the sales director, the ability to provide a detailed analysis of a used EV's battery is a crucial element in closing a deal. He said most of his clients request this data before making a decision. His business relies on SOH paperwork produced by ClearWatt, a different company in the battery analytics field.

He emphasized that these reports are entirely independent and that his team cannot alter them. This transparency builds trust with customers. He finds that once a potential buyer has seen a clear, independent report on the battery's health, it facilitates the purchase in nine out of ten instances. This openness removes a major point of friction and allows customers to buy with much greater confidence.

The Viability of Battery Repair   

In the past, the prospect of a failing EV battery was terrifying for owners, who imagined enormous replacement bills. However, the reality is often less dramatic. Matt Cleevely, who serves as managing director at the Cheltenham dealership, adds that replacing an entire battery pack is often unnecessary. It is frequently feasible to exchange only certain clusters of failing modules or cells within a battery unit.

This modular approach to repair is significantly more affordable than fitting a brand-new battery. It makes owning a used EV a much less daunting financial proposition. As the EV repair industry matures, the knowledge and tools required to perform these intricate repairs are becoming more widespread. This development is crucial for the long-term sustainability and affordability of the second-hand electric vehicle market.

Best Practices for Battery Care

The question of how to best care for an EV battery to maximise its lifespan is a common one. Simona Onori from Stanford University suggests that there is probably an optimal balance between regular rapid charging and forgoing it entirely. While convenient, consistently using high-powered DC fast chargers can put more strain on a battery over time. She did mention, however, that based on what she knows, this specific area has not yet been investigated in depth.

General advice from manufacturers and EV experts often includes a few key tips. They recommend avoiding regular charging to 100 percent or letting the battery level drop to zero. Many suggest keeping the state of charge between 20 and 80 percent for daily use. This simple habit can significantly reduce stress on the battery's chemistry and help to preserve its health over the long term.

Rapid Advancements in Technology

Despite the hesitation of some consumers, there have been remarkable advances in battery technology over the last few years. Max Reid, who is in charge of battery cost analysis at the market research company CRU, states the scale of this progress. He explained that previous generations of batteries could be expected to last for 500 to 1,000 charging events.

In stark contrast, some of the latest EV cells being released are engineered to endure 10,000 cycles. This exponential leap in durability means that newer electric vehicles entering the used market will have power packs that are far more resilient to degradation. This ongoing innovation is steadily eroding the issue of battery lifespan, making used EVs an increasingly reliable choice for consumers.

A Second Life for Old Batteries

Even after a battery is unsuitable for powering a car, it retains significant value. According to Paul Chaundy from the Dorset-based company Second Life EV Batteries, power packs that are no longer fit for their original automotive purpose can find new uses. Batteries with a State of Health under the 70 or 80 percent threshold for automotive use can still have a long and useful second life in stationary energy storage applications.

He gave an example of business clients who give old electric vehicle batteries a new purpose as energy storage at their facilities. These companies might operate six electric forklifts, yet their grid connection may only support two or three charging stations simultaneously. A repurposed battery system can store cheaper off-peak electricity and use it to charge the entire fleet without needing a costly grid upgrade.

Powering a Sustainable Future  

The repurposing of EV batteries is a critical component of the circular economy. These batteries contain valuable raw materials, including lithium, cobalt, and nickel. Finding a second life for them reduces the demand for newly mined materials and prevents old batteries from ending up in landfill. They can be used to store energy from solar panels in homes or to help balance the electricity grid on a larger scale.

This growing industry provides a sustainable end-of-life solution for automotive batteries. It maximises the utility of every component and contributes to a more resilient and environmentally friendly energy system. As the number of electric vehicles on the road continues to grow, the second-life battery market is set to expand dramatically, creating new economic opportunities and environmental benefits.

The Call for Standardisation

One of the biggest challenges remaining in the used EV market is the lack of consistency in how battery health is reported. Different automotive companies employ varying methodologies and algorithms to create SOH data for the cars they build. This can make it difficult for consumers to compare different models accurately. Mr Chaundy believes that the industry needs more standardisation in this area.

A universally accepted standard for battery health reporting would create a level playing field. It would give consumers, dealers, and technicians a clear and reliable way to assess a vehicle. The idea of a "battery passport," which would log the history and condition of a battery over its entire lifespan, is gaining traction in Europe and could provide the transparency the market needs to mature fully.

Navigating the Used EV Market

For now, buyers venturing into the second-hand EV market should arm themselves with knowledge. It is essential to look beyond the car's cosmetic condition and focus on the power source. Requesting an independent battery health report from a reputable firm like Aviloo or ClearWatt should be a standard part of any pre-purchase inspection. This simple step can provide peace of mind and prevent costly surprises down the road.

Buyers should also consider the car's battery warranty. Most manufacturers offer an eight-year, 100,000-mile warranty that guarantees the battery will retain a certain percentage of its original capacity, typically 70 percent. A used car that is still within this warranty period offers a significant safety net for the new owner, protecting them against premature battery failure.

The Road Ahead

The journey to electric mobility involves a learning curve for everyone. As the technology evolves, so too will the second-hand market. The anxieties that currently exist around battery health are likely to diminish as newer, more durable batteries become the norm in used vehicles. The growth of independent diagnostics and transparent reporting will empower consumers to make informed choices.

The shift from the roar of an engine to the hum of an electric motor is changing not just how we drive, but how we buy and sell cars. The focus has moved from mechanics to chemistry, from mileage to megawatt-hours. For the savvy buyer, the pre-owned electric car market offers the chance to embrace a cleaner, more sustainable form of transport at an affordable price. The key is simply knowing what to look for.