EV Battery SoH: What It Means and How to Check It

Knowing your battery’s state of health isn’t just useful when buying a used EV. If you already own one, checking its battery can show how quickly it is degrading, help identify a potential warranty issue, and provide valuable proof of battery condition when it’s time to sell.

But what is a good SoH value for an EV battery? How quickly does an EV battery normally degrade, and how can you check its health? We explain what the value means, how to measure it, and what you can do to help slow down battery degradation.

Key facts at a glance:

• SoH (State of Health) shows how much of an EV battery’s original capacity is still available.

• There is no universal “good” SoH value. Age, mileage, battery chemistry, and the rate of degradation all matter when judging battery health.

• EV batteries age even when they are not used. Time, temperature, and spending long periods at a very high state of charge can accelerate degradation.

• You can check the SoH in different ways, either through your car itself or with a professional battery test.

• How you charge can also make a difference. Regular AC charging and avoiding long periods at a very high state of charge can help slow down degradation.

SoH stands for State of Health and shows, as a percentage, how a battery’s condition compares with when it was new. Unlike the battery percentage you might check before leaving for work or check when deciding whether you need to charge before a longer trip, SoH indicates how much of the battery’s original capacity remains. Battery capacity simply means how much energy a battery can store and is usually measured in kilowatt-hours (kWh). 

While SoH (State of Health) describes the condition of the battery compared with when it was new, SoC (State of Charge) indicates how full it is at this particular moment. 

• SoC is the number you monitor every day as it drops on your commute, goes back up when you plug in at home, and might determine whether you stop to charge on a road trip.

• Battery SoH over time generally changes quite slowly. You probably won’t notice a difference from one week to the next, but over the years it can gradually decline as the battery ages.

Battery SoH helps you understand how well your EV battery is holding up as it ages. It shows how much of its original capacity is still available, which is useful whether you’ve been driving your EV for years or are checking out a used one.

Knowing the SoH can help you:

• Understand capacity and range loss

• See whether the battery is ageing as expected

• Spot a possible warranty issue

• Make a more informed decision when buying a used EV

• Document the battery condition when selling your EV

Just remember that SoH doesn’t tell the whole story on its own. A figure like 90% only becomes meaningful when you consider things like the car’s age, mileage, battery type, actual range, and how the SoH was measured.

The SoH gives you an important indication of the condition of your EV battery. A value of 90%, for example, means that 90% of the battery’s original capacity is still available. However, whether this is a good value for your vehicle depends on factors such as its age and mileage, battery chemistry, the test method used, and its actual range.

For a relatively new EV, an SoH close to 100% is perfectly normal. However, as the EV battery ages, it gradually loses some of its capacity. This means that a lower SoH in an EV that is more than five years old, for example, is not automatically a cause for concern. The following ranges can serve as a rough guide to help you understand what different SoH values may mean:

It’s much easier to understand percentages when they are translated into energy. Let’s do just that. An example of an electric car with a 60 kWh battery:

• 90% SoH: approximately 54 kWh usable capacity

• 80% SoH: approximately 48 kWh usable capacity

• 70% SoH: approximately 42 kWh usable capacity

How much the battery degradation affects you depends heavily on the EV. A 10% capacity loss in a long-range model with a large battery, such as a Hyundai IONIQ 6 or Tesla Model Y, may have little impact on your daily commute. The same 10% loss can be much more noticeable in an older EV with a smaller battery and limited range to begin with, such as an early Nissan Leaf with a 30 kWh battery.

A low SoH doesn’t automatically mean your EV needs a new battery. Even below 70%, the battery can still do its job. You’ll simply have less range than you did when the car was new.

So when does it actually make sense to replace an EV battery? Usually, it’s when the reduced range starts getting in the way of everyday life, there are other problems with the battery, or a manufacturer’s test finds an issue that may be covered by the warranty. The SoH number alone doesn’t decide when a battery’s time is up.

Most modern EV batteries lose only a small share of their capacity each year, but there is no magic number that applies to every vehicle. How quickly your car ages depends on the battery chemistry, temperature, mileage, charging habits, and even how well the car manages battery temperature.

And degradation doesn’t happen at exactly the same pace year after year. A battery may lose capacity a little faster at the beginning and then settle into a slower decline.

So, high mileage doesn’t necessarily mean a tired battery. ADAC’s long-term test is a nice example: a Volkswagen ID.3 still had around 91% of its original usable battery capacity after more than 170,000 km.

EV battery SoH declines because batteries naturally age over time and through use. This degradation is usually divided into two main types: calendar ageing and cycling ageing.

• Calendar ageing happens even when the car is just sitting in your driveway. Chemical reactions inside the battery continue whether you're driving or not. High temperatures and leaving the battery at a very high state of charge for long periods can speed up this process.

• Cycling ageing happens as you charge and discharge the battery. Every trip to work, weekend drive, and charging session contributes a tiny bit to this process. How quickly it happens depends on factors such as temperature, charging power, and how deeply the battery is regularly charged and discharged. Interestingly, research around bidirectional charging suggests that modern EV batteries can handle plenty of extra charging cycles, especially at lower power.

In a 2025 Geotab study, EVs charged predominantly at more than 100 kW DC lost around 3.0% of battery capacity per year on average. In contrast, EVs charged predominantly with AC or at lower charging power lost around 1.5% per year.

According to the study, fast DC charging is not inherently critical, so you don’t have to avoid it entirely. It becomes a problem when you charge at very high power all the time. So, when you’re not in a hurry, choosing AC charging can be one way to extend your battery lifespan.

For everyday charging, AC is often the more practical choice anyway. Whether at home, at work, or elsewhere, your car is often parked for hours, so charging speed matters much less. At home, an AC wallbox such as the go-e Charger makes this particularly easy: you can simply plug in when you get home and let the car charge while you sleep.

There are three main methods to check the battery state of health: from an electric car manufacturer, from independent companies specialising in it, or by yourself. Let’s have a look at the pros and cons of each option.

Tesla, Nissan, and other EV manufacturers offer battery checks. In a Tesla, for example, you can see an estimate of your battery’s remaining capacity on the touchscreen. You can also run a battery health test, which requires the car to stay connected to an AC charger for up to 24 hours. The result shows how much energy the battery can still store compared with when it was new. Such tests or battery health information provided directly by the car manufacturer are often available for free.

Companies like DEKRA offer completely independent battery checks. Normally, they must be performed by a professional, so you need to find a vehicle inspection station where this service is offered. The battery check from DEKRA costs between €90 and €150.

The AVILOO device is connected to the vehicle, and the test can begin once the electric car is fully charged. The driver then has seven days to discharge the battery to below 10% without recharging. However, there is no minimum test duration, so you can also use up the battery in one go. 

Now, how does this device get installed in your vehicle? There are two options. You can ask a technician at a service centre to install it or, if you feel confident doing it yourself, have the test box sent to you for self-installation.

AVILOO also offers a battery warranty with its quick Flash Test, which, unlike the more detailed Premium Test, requires no battery discharge. The warranty lasts for one year or 20,000 km, with a minimum SoH set for your specific car. If the battery drops below it, you get €3,000 in compensation, and the Flash Test cost back.

Results from AVILOO, DEKRA, or other independent providers can help you decide whether it’s worth contacting your dealer, especially if your EV range has recently dropped more than expected. However, the manufacturer is the one deciding whether you actually have a valid warranty claim and usually requires the battery to be tested according to its own inspection method.

Evaluating an SoH percentage only makes sense when paired with the car's age, mileage, and charging history. What counts as “healthy” can look quite different depending on the vehicle. Here’s what is important for you to consider:

• There is no universal annual degradation rate. Large studies suggest that modern EV batteries generally lose only a small percentage of their capacity each year, but the actual rate varies considerably between vehicles. Temperature, battery chemistry, thermal management, charging habits, and mileage can all play a role.

• Put SoH into context with vehicle age and mileage. You’d naturally expect a fairly young EV to be closer to its original capacity, while some degradation after years on the road is completely normal. So don’t let the warranty threshold be your only benchmark. A four-year-old EV with 72% SoH may still be above the roughly 70% limit used in many battery warranties, but that doesn’t necessarily mean everything is fine. 

• High mileage doesn’t automatically mean a worn-out battery. DEKRA’s findings from thousands of battery tests include high-mileage EVs that still retained a surprisingly large share of their original capacity. So, when buying a used EV, mileage alone tells you relatively little about the actual condition of the battery.

• Consider the original battery capacity size. The same percentage loss doesn’t always feel the same on the road. Lose 10% from a large 77 kWh battery and you may simply give up a few dozen kilometres of range. Lose the same 10% from an older 24 kWh city EV, and those missing kilometres can matter a lot more between charging stops.

You can help your EV battery age more slowly by charging it in a way that suits its battery type, avoiding unnecessary heat and not relying on fast charging when you don’t need it. That might sound like a lot to remember, but in everyday life, it comes down to a few pretty simple habits.

1. Know what kind of battery your EV has. There’s no charging rule that works perfectly for every EV. For NMC and NCA batteries, keeping the charge roughly between 20% and 80% in everyday use can be a good approach. LFP batteries are more tolerant of higher states of charge and can generally be charged to 100% more regularly.

2. Save 100% for when you actually need it. A full charge makes sense before a long journey. For the usual commute or a weekend spent mostly in the driveway, there’s little reason to keep it sitting at 100%.

3. Choose AC charging when there’s no rush. DC fast charging is very handy on a road trip, and using it occasionally is perfectly fine. But for everyday charging, AC is the gentler option. Your battery probably doesn’t need a 15-minute pit stop while you’re asleep anyway.

It’s not only about choosing AC over DC. When and how you charge can make a difference too. For example, leaving your EV at a very high state of charge for long periods can speed up calendar ageing. The good news is that you don’t need to watch the battery percentage all day or completely change your routine. A smart wallbox can make a few battery-friendly habits easier to fit into everyday life:

• Adjust the charging current: If your car is going to be parked in the garage all night anyway, there is often no need to charge at the highest available power. You can lower the charging current and simply let the car charge while you sleep.

• Schedule charging: If you know you normally leave at 7:30 in the morning, you can schedule charging closer to that time instead of having the battery reach a high state of charge hours earlier and then sit there until you leave.

But don’t let battery health turn into another thing to worry about every time you plug in. Sometimes you need 100% before a long road trip. Sometimes you need a DC fast charger because you want to get back on the road. That’s what they’re there for. Battery-friendly charging is more about the habits you follow most of the time than about avoiding every situation that could put a little more stress on the battery.