Electric vehicle battery guide for fleets

How long does an electric car battery last? Use Geotab’s free electric vehicle battery degradation comparison tool to compare the average battery degradation over time for different vehicle makes and model years. Geotab developed the tool based on an analysis of 6,300 fleet and consumer electric vehicles, representing 1.8 million days of data. 

Get started with the tool

Read our guide to learn all about EV battery health, including what you can do to improve it and extend your electric car battery life, and get key takeaways from our tool on real-world battery performance.

The importance of EV batteries

If you’re thinking about buying an electric vehicle (EV), there are some important factors to consider. But there are probably  three questions that are at the top of your list:

• How much will the EV cost?
• What is its range?
• How long will the battery last?

From a life-cycle perspective, battery performance and health really are the key to it all. As the battery is the most expensive part of an EV, battery health doesn’t just affect the vehicle’s residual value (helping to answer the cost question), but it also has a direct impact on your EV’s maximum usable range over time.

How long will an electric car battery last?

This can be a tough question to get a straight answer to. What you may find instead are statements that batteries are covered by warranty should something go wrong. Typically, battery coverage is 8 years/100,000 miles, but this varies by manufacturer and country.

Reassuringly, battery costs are falling  year over year. Since 2010, the price of an average Lithium-ion battery pack has dropped by over 80%.

An automaker’s guarantee of their battery technology and the promise of decreasing costs should inspire some confidence. However, wouldn’t it be much better to know how quickly your battery is expected to degrade, and how to minimise this loss?

What is EV battery degradation?

Battery degradation is a natural process that permanently reduces the amount of energy a battery can store. 

A battery’s condition is called its state of health (SOH). Batteries start their life with 100% SOH and over time they deteriorate. SOH is a measure of how much energy the battery can deliver (kWh).

This isn’t the same as vehicle range (distance the vehicle can travel on those kWhs) — which will vary on a daily or trip-by-trip basis, depending on a number of factors including charge level, temperature, driving habits, and passenger or cargo load.

Common factors impacting lithium-ion battery health:

1. Battery age
2. High temperatures
3. Operating at high and low state of charge
4. High electric current
5. Usage (energy cycles)

While there has been plenty of research done on battery health, there has been very little data following the real-world performance of EVs over time, let alone comparisons across different makes and models. 

Until now.

Introducing the Electric Vehicle Battery Degradation Tool

Geotab created the Electric Vehicle Battery Degradation Tool to assess how batteries have been holding up and to consider the relative importance of the above factors on electric car battery life under real-world conditions.

We analysed the battery health of 6,300 fleet and consumer EVs, representing 1.8 million days of data. From the telematics data processed, we have gained insight into how real-world conditions influence the battery health of electric vehicles, providing data for 21 distinct vehicle models, representing 64 makes, models, and years.

Notes about the tool:

• The degradation curves displayed below are the average trend line from the data analysed.
• These graphs can offer insight into average battery health over time, but should not be interpreted as a precise prediction for any specific vehicle.
• A subset of vehicle makes, models, and years are not available in the visualisation tool— we have excluded vehicles with insufficient data. (Don’t be alarmed if your car of choice is missing!)

Get started with the tool

What the tool has taught us about EV battery health 

EV batteries are remaining healthy

Based on data from over 6,000 electric vehicles, spanning all the major makes and models, we found that batteries are maintaining high levels of health. If the observed degradation rates are maintained, most batteries will outlast the usable life of the vehicle.

Battery health declines with age

As you might expect, the older a vehicle is, the more likely its battery has deteriorated. However, when looking at average decline across all vehicles, the loss is still really low at 2.3% per year. This is good news! If you purchase an EV today with a 150 mile range, you’ll only lose about 17 miles of range after five years, which is unlikely to impact your day-to-day needs.

EV battery degradation isn’t linear

While our tool shows more or less linear degradation, we know that EV batteries generally decline non-linearly: an initial drop, then a longer, more moderate pace of decline, followed by a more significant drop in battery health at its end of life. 

Figure 1: A normal degradation curve is expected to look something like this.

You’ll be pleased to know that we’ve still seen very few batteries reach their end-of-life drop. This means that we can’t yet predict quite when this will happen, but we’ll keep monitoring to find out. 

There’s a big difference between makes, models and years

Our data shows us that EV batteries respond differently to the test of time, depending on their make and model-year. There are two possible factors: battery chemistry and thermal management of the battery pack. 

While EVs use lithium-ion batteries, there are many different variations of lithium-ion chemistries, which will influence how the battery responds to stress. 

In addition to cell chemistry, battery thermal management techniques differ across vehicle models. Some batteries are cooled or heated by air, and others by liquid. 

Let’s compare a vehicle with a liquid cooling system (the 2015 Tesla Model S) to one with a passive air cooling system (the 2015 Nissan Leaf) The Leaf has an average degradation rate of 4.2%, while the Tesla is 2.3%. Good thermal management gives batteries better protection against degradation.

 Figure 2: Battery degradation comparison of the 2015 Tesla Model S (liquid cooling) vs. the 2015 Nissan Leaf (passive air cooling

State of Charge (SOC) 

Operating a battery at near full or empty can negatively affect battery health. To limit this effect, many manufacturers add a buffer, effectively preventing access to the extreme ends of the SOC window. 

High vehicle use isn’t a concern

One exciting piece of information we were able to glean from the data was that batteries in vehicles with high use didn’t degrade any faster. This should come as welcome news, since you don’t get the benefit of an EV if it’s just sitting in the car park.

The takeaway? Don’t be afraid to put your EVs in high-use duty cycles. As long as they are within their daily driving range, their battery life won’t be negatively impacted. Just as long as high usage doesn’t require routine DC fast charging - read on to find out why.

Figure 3: Amount of use doesn’t appear to have much impact on degradation rates.

Vehicles driven in hot temperatures decline faster

A battery exposed to very hot temperatures will be prone to more damage, but by how much? Will an EV in Arizona have a different battery life than the same car driven in Norway? To find out, we grouped the vehicles based on the following climate conditions:

• Temperate (fewer than 5 days per year over 27°C or under -5°C)
• Hot (more than 5 days per year over 27°C)

As you can see below vehicles driven in hot climates declined much faster than those driven in moderate climates. This is not great news if you and your fleet toil under the hot sun!

Figure 4: Batteries exposed to hotter climates degrade faster than those in temperate climates.

Regular rapid charging isn’t good for battery health

The regular use of fast chargers, or DCFCs, appears to impact the speed that batteries degrade. Rapidly charging a battery means high currents resulting in high temperatures, both known to strain batteries. In fact, many automakers do suggest limiting the use of DCFC to help prolong their electric vehicles’ battery life.

Here we looked at all battery electric vehicles in the same climate group , and categorised them based on how frequently they used a DCFC: never, occasionally (1-3 times per month), and frequently (more than 3 times per month).

Figure 5: Battery degradation is faster when fast chargers are used regularly

While there may be other factors at play (we want to stress that this wasn’t a controlled experiment), charging via lower power L2 charging should be prioritised.

How do I increase EV battery life?

While battery degradation varies by model, climate and charging type, the majority of vehicles on the road today haven’t experienced significant decline. In fact, overall degradation has been very slight, with an average capacity loss of just 2.3% per year. Under ideal climate and charging conditions, the loss is only 1.6%.

While some things are out of an operator’s control, there are ways you can extend the life of your EV’s battery.

Some tips for operating your EVs to keep your batteries healthier for longer:

• Avoid keeping your car sitting with a full or empty charge. Ideally, keep your state of charge (SOC) between 20-80% particularly when leaving it for longer periods, and only charge it fully for long distance trips.
• Minimise fast charging (DCFC). Some high-use duty cycles will need a faster charge, but if your vehicle sits overnight, level 2 should be sufficient for most of your charging needs.
• Climate is out of an operator’s control, but try to avoid extreme hot temperatures, for example by parking in the  shade on hot days.
• High-use is not a concern, so fleets shouldn’t hesitate to put their EVs to work. An EV isn’t useful sitting idle in the car park and putting on more miles per vehicle is overall a better fleet management practice.

Final thought: Don’t sweat the small stuff. As vehicles come out with larger battery packs, losing some capacity may not impact your day-to-day driving needs, and shouldn’t overshadow the many benefits EVs have to offer.

Planning on electrifying your fleet? Geotab customers can get a free EV suitability assessment to take the guesswork out of EV procurement. Find out which EVs will do the job and save money.

See also: What can 6,000 electric vehicles tell us about EV battery health?