The battery is at the heart of every EV, but you don’t need to be an expert to understand the basics. Knowing what battery capacity, State of Health and charging mean can help you make sense of electric vehicles and assess a used EV with more confidence. This guide covers the key terms, what affects battery condition and what to look for when considering an electric vehicle.
How Does An EV Battery Work?
An EV uses a large rechargeable battery pack to store the energy needed to power its electric motor. Instead of burning petrol or diesel in an engine, the vehicle draws electrical energy from the battery and uses it to drive the wheels.
This main battery is often called the traction battery or high-voltage battery. It is different from the smaller 12V battery also found in electric vehicles, which powers many of the car’s electrical systems.
Understanding Battery Capacity
EV battery capacity is usually measured in kilowatt-hours, or kWh. Put simply, this tells you how much energy the battery can store.
A battery with a larger capacity can generally provide more driving range than a smaller one, but battery size isn’t the only factor that determines how far an EV can travel. Vehicle weight, temperature, speed, driving conditions and energy use all have an effect.
You may also see references to gross and usable battery capacity. The gross figure is the battery’s total capacity, while usable capacity is the amount made available to the driver. Manufacturers may reserve some capacity to help protect the battery.
From The Battery To The Wheels
When you accelerate, electricity stored in the battery is supplied to the electric motor. The motor then turns electrical energy into movement.
Most EVs can also recover some energy when slowing down through regenerative braking. Instead of all that energy being lost as heat through the brakes, some can be sent back to the battery.
What Is EV Battery Health?
Just like other components in a vehicle, an EV battery changes as it gets older and is used. Battery health is a way of understanding its condition and how its current capabilities compare with when it was newer.
One of the terms you’ll often come across is State of Health.
State Of Health Explained
State of Health, usually shortened to SoH, is commonly shown as a percentage. It provides an indication of the battery’s condition compared with its reference condition when new.
As a battery ages, its ability to store energy can gradually reduce. A lower State of Health can therefore mean less usable capacity than the battery originally had.
SoH should not be treated as a direct prediction of how many miles an EV will travel. Real-world range depends on the vehicle, weather, driving conditions and several other factors.
State Of Health Vs State Of Charge
State of Health and State of Charge sound similar, but they describe two different things.
State of Charge (SoC) tells you approximately how full the battery is at that moment. If an EV has 70% charge remaining, that’s its State of Charge.
State of Health (SoH) is an assessment of the battery’s overall condition or capacity compared with its reference condition.
A simple way to think about it is that State of Charge changes every time you drive or recharge the vehicle. State of Health usually changes much more gradually as the battery ages and is used.
Do EV Batteries Degrade Over Time?
Yes. Some battery degradation is a normal part of an EV getting older.
That doesn’t mean an EV battery suddenly stops working after a certain number of years or miles. In many cases, the change in capacity happens gradually.
Current UK regulations mandate EV battery warranties of eight years or 100,000 miles, with manufacturers required to provide a replacement battery if capacity falls below 70% for cars or 65% for vans during this period.¹
Government consumer guidance also states that most EV batteries retain around 80% to 90% of their capacity after this warranty period.²
Warranty terms and eligibility should still be checked for the individual vehicle, particularly when considering a used EV.
What Can Affect EV Battery Degradation?
Several factors can influence the rate at which a battery changes over time.
Age is one. Battery cells undergo chemical changes as they get older, which can gradually reduce the amount of energy the battery is able to store.
Temperature can also matter. Very high or low temperatures can affect lithium-ion battery performance, while prolonged exposure to high temperatures can contribute to faster degradation.³
How a vehicle is charged and used can have an effect too. Manufacturers provide their own charging recommendations, so it’s worth checking the guidance for the particular make and model rather than assuming the same rules apply to every EV.
What Does Degradation Mean For The Driver?
The most noticeable effect of battery degradation is usually a reduction in usable capacity.
If a battery can hold less energy than it could when new, the vehicle may not travel as far between charges under otherwise similar conditions.
But range alone doesn’t provide a complete diagnosis of battery health. A low predicted range on the dashboard can also be influenced by cold weather, recent driving style and energy use from systems such as cabin heating.
How Does Charging Affect An EV Battery?
Charging is part of everyday EV ownership, but not every charger works in the same way.
The two terms drivers will commonly encounter are AC charging and DC rapid charging.
AC And Rapid DC Charging
Home chargers and many public chargers supply alternating current, or AC. The vehicle converts this into the direct current needed by the battery.
Rapid and ultra-rapid public chargers can supply DC electricity directly to the battery, allowing compatible vehicles to charge much more quickly.
The maximum charging speed varies between electric vehicles. It can also change during a charging session depending on factors such as battery temperature and State of Charge.
Should You Always Charge An EV To 100%?
Not necessarily.
You may have heard that an EV should always be kept between particular charge percentages. While some manufacturers recommend limiting everyday charging to help maintain battery health, the appropriate approach depends on the vehicle and its battery chemistry.
Some EVs also allow the driver to set a charging limit through the car or its app.
The safest approach is to follow the manufacturer’s guidance for that particular model rather than applying one charging rule to every electric vehicle.
Does Rapid Charging Damage An EV Battery?
Rapid charging can place different demands on a battery compared with slower charging, particularly because battery temperature needs to be carefully managed.
But modern EVs have battery management systems designed to control factors such as charging speed and temperature. The vehicle may automatically reduce its charging rate when necessary.
Using a rapid charger doesn’t therefore mean that the battery is automatically being damaged. Battery ageing is affected by a combination of factors rather than one charging session or charging method alone.
How Battery Health Can Affect EV Range And Performance
Battery health is one factor that can influence how far an EV travels between charges, but it isn’t the only one.
Your actual range can differ depending on factors such as:
- Outside temperature
- Driving speed and style
- Motorway or urban driving
- Heating and air conditioning use
- Vehicle load
- Terrain
- Battery condition
Cold weather is particularly worth understanding. Lower temperatures can temporarily reduce the performance and range available from lithium-ion batteries.³
That doesn’t necessarily mean the battery has suffered permanent degradation. A temporary reduction in cold-weather range should not automatically be treated as evidence of poor battery health.
Checking The Battery Health Of A Used EV
When looking at a used electric vehicle, age and mileage provide useful context, but they don’t tell you everything about its battery.
Two EVs of the same age and with similar mileage can have been driven, charged and stored differently. Battery information can therefore add another useful piece of evidence when assessing a vehicle.
What Should You Look For?
Start with the information available for the individual vehicle.
Depending on how and where you’re buying it, this might include service history, battery warranty information, diagnostic information or a dedicated battery health report.
If a State of Health figure is provided, remember what it represents. It gives information about battery condition, but it shouldn’t be used on its own to predict exact real-world range or the overall condition of the vehicle.
If you’re considering a damaged EV, don’t attempt to inspect, disconnect or repair high-voltage battery components yourself. GOV.UK guidance warns that damaged high-voltage components and cabling may be capable of delivering a fatal electric shock.⁴
EV Battery Health Reports At Copart
For selected EVs available through Copart UK, active Members may be able to access a free, independent EV Battery Health Report powered by AVILOO Battery Diagnostics.
Where available, the report can provide information including the battery’s State of Health, voltage performance, Battery Control Unit health, battery-to-vehicle communication and charging insights.
You can learn more about EV Battery Health Reports at Copart UK.
Reports can be viewed and downloaded through the Reports and Services section of the Lot Details page where available.
The EV Battery Health Report should be considered alongside the other information available for the Lot, including its images, description, documents and Lot Details. It is one part of the checks you can make before deciding whether to bid.
What Happens When An EV Battery Gets Older?
An ageing EV battery doesn’t automatically reach a point where the complete battery pack suddenly needs replacing.
A battery may continue to operate while offering less usable capacity than it did earlier in its life. The significance of that reduction will depend on the vehicle and how it is being used.
Current UK requirements provide battery warranty protection for qualifying electric vehicles, while government guidance also states that most EV batteries retain around 80% to 90% capacity after the eight-year or 100,000-mile warranty period.¹ ²
Where battery work is required, the appropriate solution will depend on the design and condition of the pack. Government guidance notes that EV batteries can be recycled, and some may also have uses outside vehicles after their automotive life.¹
Understanding An EV Before You Bid
Battery terminology can look complicated at first, but a few measurements make it much easier to understand.
State of Charge tells you how much charge is currently available. State of Health gives an indication of battery condition. Battery capacity tells you how much energy the pack can store, while factors such as temperature, driving conditions and vehicle use help determine how far that energy will take you.
For a used EV, battery information can add useful context, but it should form part of a wider assessment of the vehicle rather than being viewed in isolation.
Frequently Asked Questions
How Long Does An EV Battery Last?
There isn’t one fixed lifespan for every EV battery. Battery condition changes gradually and is affected by factors including age, temperature and use.
UK regulations mandate battery warranties of eight years or 100,000 miles, while government consumer guidance states that most batteries retain around 80% to 90% capacity after this warranty period.¹ ²
What Is A Good State Of Health For An EV Battery?
A higher State of Health generally indicates that more of the battery’s original capacity remains, but there isn’t one percentage that defines a “good” battery for every EV. The vehicle’s age, battery type, intended use and the way SoH has been measured all need to be considered.
What Is The Difference Between State Of Health And State Of Charge?
State of Charge tells you how full the battery currently is. State of Health provides an indication of the battery’s condition compared with its reference condition. State of Charge can change substantially in a single journey, while State of Health normally changes gradually.
Does Rapid Charging Damage An EV Battery?
Rapid charging doesn’t automatically mean an EV battery will be damaged. Modern electric vehicles have battery management systems that can control charging speed and battery temperature. Battery degradation is influenced by several factors over time.
How Can I Check The Battery Health Of A Used Electric Vehicle?
Look for battery diagnostic information or a battery health report where one is available. A State of Health measurement can provide useful information, but it should be considered alongside the vehicle’s age, history, condition and other available documentation.
For selected EVs at Copart UK, an independent AVILOO EV Battery Health Report may be available through the Lot Details page.
Does Cold Weather Damage An EV Battery?
Cold temperatures can temporarily reduce lithium-ion battery performance and available range.³ This shouldn’t automatically be confused with permanent battery degradation, as performance can change again as temperatures change.
Understanding battery health can make it easier to assess an EV and decide whether a particular vehicle suits what you’re looking for. Visit Copart UK’s Vehicle Finder to explore electric vehicles currently available through our auctions.
Sources
¹ Office for Zero Emission Vehicles, Electric Vehicles: Costs, Charging and Infrastructure.
² UK Government Clean Energy Campaign, Get an Electric Vehicle.
https://cleanenergy.campaign.gov.uk/electric-vehicle/
³ London Fire Brigade, Heat, Cold and Rain: How Weather Conditions Affect E-Bikes and E-Scooters.
⁴ Driver and Vehicle Standards Agency, MOT Inspection Manual: Cars and Passenger Vehicles – Lamps, Reflectors and Electrical Equipment.