The traction battery is one of the most important and valuable components in an electric vehicle. It stores the energy used to power the electric motor and has a direct impact on how far the car can travel between charges.
Like every rechargeable battery, an EV battery gradually changes as it ages. Its usable capacity can decrease over time, which is why EV battery health becomes increasingly important as a vehicle gets older.
Some degradation is completely normal and does not mean that the battery is faulty. However, understanding its condition can be useful when investigating range loss, charging problems or assessing a used electric vehicle.
So how can EV battery health actually be checked?
Battery health is a way of describing the current condition and usable capability of a battery compared with its condition when new.
You may see this represented as State of Health (SOH).
A new battery begins with a certain usable capacity. As it experiences charging cycles, temperature changes and natural chemical ageing, the amount of energy it can store may gradually decrease.
For example, a battery that originally offered 60 kWh of usable capacity may provide less after many years of operation.
This gradual reduction is known as battery degradation.
Importantly, reduced capacity does not automatically mean the battery has failed. An older EV can remain perfectly usable even when its battery no longer provides the same range it did when new.
Yes.
Lithium-ion batteries naturally degrade with time and use. There is no realistic way to keep an EV battery at exactly the same condition indefinitely.
Manufacturers design battery packs and their management systems to control this process.
EVs generally do not allow drivers to use every theoretical kilowatt-hour contained within the battery. Some capacity may be reserved to protect the cells from extreme states of charge.
Battery management systems also monitor temperature, voltage and charging behaviour to keep the battery within appropriate operating limits.
The question is therefore usually not whether an EV battery has degraded at all, but whether the level of degradation is normal for its age and use.
There is more to battery health than simply looking at the range displayed on the dashboard.
Professional EV battery diagnostics can provide access to information from the battery management system and other vehicle control modules.
Depending on the manufacturer and vehicle, an assessment may include:
The exact information available varies considerably between vehicles.
For this reason, EV battery assessment is not always as simple as connecting a scanner and reading one percentage.
The estimated range displayed by an EV can provide some useful information, but it is not a direct measurement of battery health.
The vehicle calculates predicted range using several variables.
These can include:
If you spend a week driving short journeys in cold weather with the heating on, the estimated range may fall significantly even though the battery has not suddenly deteriorated.
Similarly, efficient driving in favourable conditions can produce a much higher estimate.
Dashboard range should therefore be treated as an estimate of how far the car may currently travel, not a definitive measurement of battery condition.
Battery degradation is one possible reason, but there are many others.
Cold weather is a common example. Low temperatures affect battery performance and increase the amount of energy required to heat the cabin and, in some vehicles, the battery itself.
Driving at sustained motorway speeds also consumes considerably more energy than slower urban driving.
Other factors include tyre pressures, vehicle load, use of climate control and changes in driving style.
If range loss is significant, persistent and cannot be explained by operating conditions, battery diagnostics can help determine whether the traction battery itself is contributing to the problem.
Battery degradation is influenced by both calendar ageing and cycle ageing.
Calendar ageing occurs simply as the battery gets older. Even a low-mileage EV will experience some chemical changes over time.
Cycle ageing is associated with charging and discharging the battery through normal use.
Several other factors can influence the rate of degradation, including battery chemistry, temperature, charging habits and the way the vehicle manages its battery.
This is why two electric cars with identical mileage do not necessarily have identical battery health.
DC rapid charging places different demands on a battery compared with slower AC charging, particularly because significantly higher charging power can generate more heat.
However, modern EVs actively manage charging power and battery temperature to protect the pack.
Occasional or regular rapid charging does not mean that a battery will suddenly become damaged.
The long-term effect depends on factors such as battery chemistry, thermal management, charging frequency, temperature and the manufacturer’s battery control strategy.
For most drivers, using rapid charging when it is needed is part of normal EV ownership.
Charging to 100% is not automatically harmful, and manufacturers design their vehicles to manage the battery within defined operating limits.
However, some battery chemistries may benefit from avoiding extended periods at a very high state of charge when full capacity is not required.
Many EV manufacturers therefore allow owners to set a daily charging limit, often somewhere below 100%.
At the same time, recommendations differ between vehicles and battery chemistries. Some manufacturers may specifically recommend regular full charges for certain battery types.
The best approach is to follow the charging guidance provided for your particular vehicle rather than applying one universal rule to every EV.
EV batteries work best within a suitable temperature range.
Excessive heat can accelerate battery degradation, while very low temperatures can temporarily reduce performance and charging capability.
Modern electric vehicles may use sophisticated thermal management systems involving coolant circuits, pumps, valves, sensors and other components to regulate battery temperature.
A fault in this system can therefore affect battery performance and charging behaviour.
HybridElectric Manchester provides specialist hybrid and EV cooling system repair where thermal management problems affect electrified vehicle systems.
Yes.
An EV traction battery contains many individual cells arranged into modules or other groups depending on the battery design.
These cells need to operate together.
If one section begins behaving significantly differently from the others, the battery management system may detect an imbalance or abnormal voltage behaviour.
A problem affecting a relatively small part of the pack can therefore influence the operation of the complete battery.
This is why detailed diagnostic data can be more informative than a single overall health percentage.
There is no single percentage that should be treated as universally “good” or “bad”.
A battery with less than its original capacity may still provide perfectly adequate range and operate normally.
Its condition needs to be considered in context, including:
The difference between normal degradation and an actual battery fault is particularly important.
A battery that has gradually lost some capacity over many years is a different situation from a pack containing an abnormal cell group or displaying high voltage system faults.
It can be a very useful part of assessing a used electric vehicle.
Mileage and age provide some information, but neither tells you exactly how the battery has aged.
Two apparently identical used EVs can have different battery conditions depending on their history and operating environment.
An assessment of the traction battery can provide additional information about its current condition and reveal abnormalities that may not be obvious during a short test drive.
It should still form part of a wider inspection of the vehicle rather than being the only factor considered when making a purchase.
Not automatically.
Battery degradation and battery failure are different things.
A reduction in usable capacity may simply mean that an older vehicle provides less range than when it was new. If that range still meets the owner’s needs and the battery operates correctly, immediate replacement may not be necessary.
Actual faults require a different approach.
Problems involving individual battery components, the battery management system, high voltage connections or thermal management need to be diagnosed to determine what repair is appropriate.
If testing identifies a separate fault within the vehicle’s high voltage network, specialist high voltage system repair may be required instead of work on the battery pack itself.
Poor battery health is only one possible explanation for charging problems.
An EV also relies on its charge port, onboard charger, electrical connections, communication systems and associated control electronics.
If the car fails to charge, repeatedly interrupts charging or behaves differently depending on the charging source, the complete vehicle-side charging system may need to be investigated.
Our charging system diagnostics and repair service is designed specifically to identify these types of faults.
There is usually no need to continually test a battery that is operating normally.
A battery assessment becomes particularly useful when there is a reason to investigate its condition.
This could include noticeable unexplained range loss, battery warnings, unusual charging behaviour or concerns about an older vehicle.
It can also provide useful information when evaluating a used EV or planning to keep an electric vehicle for many more years.
Battery health should be viewed as one part of understanding the condition of the vehicle rather than a number that needs to be checked after every few thousand miles.
EV battery health cannot be judged accurately from mileage or dashboard range alone.
The battery’s age, operating data, temperature behaviour, charging history and condition of individual sections can all contribute to the overall picture.
HybridElectric Manchester provides specialist EV battery diagnostics to investigate battery health, performance and faults affecting electric vehicles.
If you have noticed unexplained range loss, battery warnings or unusual behaviour from your EV, contact our team to arrange a battery assessment.
HybridElectric Manchester is part of the European HybridElectric network, providing specialist diagnostics and repairs for hybrid and electric vehicles.