Your Guide to EV Batteries: Premature Death, Range Loss and Preservation
The topic of electric car batteries has countless facets, from the types of cells and various chemistries to the prospects for future improvements, but it’s unlikely that any shopper would choose an electric vehicle based on whether its battery pack uses, say, cylindrical instead of pouch-style cells. So we’ll do what Cars.com always attempts to do, which is focus on what matters right now to current shoppers and owners. Speaking of focus, shoppers have concerns about EV batteries — and they should — but those concerns often focus on the wrong thing. Let us steer you toward the issues worth considering.
- Premature Death and Replacement
- Range Loss Is Guaranteed by Age
- Extreme Temperatures Obliterate Range … in Different Ways
- DC Fast Charging Compromises Battery Life
- How to Preserve Your EV’s Battery Capacity and Range
- Don’t Shop by Kilowatt-Hours
Related: More EV News and Advice
Premature Death and Replacement
Let’s get this out of the way. Shoppers correctly surmise that the battery packs in electric cars are very expensive parts and thus prohibitively expensive to replace, but there’s a misconception that they’re likely to fail someday. There’s no question that their cost would make the typical owner walk away from the car altogether rather than replace a battery pack. (Most individuals won’t bother having a conventional vehicle’s engine or transmission rebuilt, a cheaper endeavor than battery replacement, even though the used-car market happily rebuilds those components and resells the cars if their owners give them up.) But complete battery pack failure is rare. We learned the same thing over the course of 20 years after hearing the same concerns about gas-electric hybrids. Further, electric cars have powertrain warranties amounting to at least 100,000 miles or eight years, as required by law, so in the event of failure, the battery should be covered for the original owner (used-EV buyers should always make sure the warranty transfers to them before buying). Battery death is not worth worrying about unless you’re buying a used EV or are someone who insists on keeping a vehicle for decades, for both this reason and those below.
Range Loss Is Guaranteed by Age
What all EV shoppers and owners should be aware of, even concerned about, is that all rechargeable batteries lose capacity with use and time, even if you do everything right. For what it’s worth, most modern EVs are designed to do things right to ensure that your car never behaves like a two-year-old smartphone, and there’s even more an owner can do (more on that below). But it’s inevitable that a battery’s capacity — meaning the car’s range — will diminish over time. Anyone considering one of these cars and determining how much range they will need should know and account for this.
In the earlier days, automakers clearly stated in owner’s manuals that EVs would lose capacity over time. For example, the manual for the 2011 Nissan Leaf Cars.com purchased in 2011 warned:
“Nissan estimates that battery capacity will be approximately 80% of original capacity after five years, although this is only an estimate and the percentage may vary (and could be significantly lower) depending on individual vehicle and Li-ion battery usage.”
If this were true, it would mean the Leaf’s initial EPA-estimated range of 72 miles would be 57.6 miles, and after 10 years, if the degradation remained consistent, the range would be 43.2 miles. The 2017 Chevrolet Bolt EV’s manual said, “Depending on use, the battery may degrade as little as 10% to as much as 40% of capacity over the warranty period.”
We’ve learned more since then from various studies and companies that collect data from real vehicles in the hands of consumers. Recurrent, a platform that monitors more than 7,000 connected vehicles in the U.S. (so far) and offers used-EV reports for shoppers, suggests that EV batteries lose less capacity than the worst cases predicted above by Chevy and Nissan.
“Every electric vehicle loses range differently, including cars of the same brand or year,” said Recurrent CEO Scott Case. “The good news, however, is that several early EV models show us that batteries last longer than people expect. Across all of the EV models that we track in the US, there is a noticeable S curve in the data, where cars lose a few percentage points of range from their original EPA estimate relatively quickly, generally in the first two years, then range loss levels off for the next several years as the battery stabilizes. After five years, it is common to see a 5-10% drop in range. Some vehicle models follow a fairly linear 1.5-2.0% per year, while most others drop 2-3% in the first couple of years before leveling to 1% per year. In the Tesla Model S, for example, we see that many lose less than 5% of range from 50,000 to 200,000 miles.”
Based on the 10% drop after five years, which is the higher end of Recurrent’s range, we’re looking at closer to a 20% loss by the time an original battery warranty expires, presuming that the degradation continues at the same pace. (A better performer would be closer to 10%.) Geotab, an Ontario-based company that tracks battery health in many EVs, including commercial fleet models, pegs average battery degradation at 2.3% per year. For supporting evidence, look no further than EV manufacturers, some of whose battery warranties guarantee 70% of the original capacity within the warranty period, which seems to agree with the potential for 80% to remain, plus an extra 10% safety margin to account for the many variables that could result in worse-than-average range loss. According to Recurrent, warranty claims based on capacity loss are rare.
To illustrate how differently EV battery packs can age, Recurrent has seen low-mileage used EVs with less than half their original range and nine-year-old cars with nearly all of their original EPA-rated range. The variability is based on the make and model, how they’re charged and driven, the temperatures to which they’re subjected and even more factors, unfortunately. Read on to learn what some of these issues are and what you can do to get the most out of your EV’s battery.
Extreme Temperatures Obliterate Range … in Different Ways
It’s no coincidence that EVs have been most popular in warmer climates. Their range diminishes temporarily in colder temperatures. And that’s all electric cars.
It’s both because their battery packs lose capacity when they’re colder and because cabin heat is necessarily electric, which robs range. In 2011, our Nissan Leaf with an EPA-estimated 73 miles of range dropped to around 50 miles during winter in Chicago. A AAA study has since quantified the range loss at 20 degrees Fahrenheit to be roughly 40% lower than at 75 degrees for the average EV.
So this is an important consideration if you’re determining how much range you need and you live in a colder climate. You can maximize your range by preheating the cabin while the car’s still plugged in, using grid power, but the overall effects of cold on range are unavoidable.
Also, lithium-ion batteries work below freezing but they don’t like charging at that temperature. This doesn’t mean they can’t be charged, but charging might be slower and less efficient as the car uses some energy to keep the battery warm. Regenerative braking might also be compromised by subzero temps, depending on the model, because that also constitutes charging.
The good thing about normal winter cold is that its effect on battery capacity is temporary. High temperatures, on the other hand, can result in accelerated capacity loss. Though this is a widely known phenomenon, the degree isn’t well known, as usual, because there are so many variables involved. According to Geotab data, after four years, an EV in a temperate climate shows less battery degradation than one in a hot climate, but the difference is less than a quarter of a percent. Perhaps it’s because Geotab’s division between temperate and hot climates is simply fewer or more than five days per year over 80 degrees F. Or perhaps it’s because almost all EVs sold today have active thermal management — liquid cooling (and often heating) of the battery pack, which keeps it healthy and efficient, especially when plugged in to charge.
A comparison of one 2015 model EV without active thermal management, the Nissan Leaf, with another 2015 that has it, the Tesla Model S, might be the most useful: Geotab reports the Leaf’s average degeneration rate at 4.2% and the Model S’ at 2.3%.
Note that driving an EV in high temperatures also diminishes range temporarily, but the degree isn’t as pronounced as with cold. Where’s the sweet spot? A battery temperature around 70 degrees F.
DC Fast Charging Compromises Battery Life
With almost no exceptions, EV manufacturers enable public DC fast charging (sometimes called Level 3) but warn that it’s best done sparingly to prevent premature capacity loss. Once again, “sparingly” defies definition and numbers regarding the potential degradation are elusive. The most definitive figure we’ve seen was from Kia, which attributed 10% degradation over eight years to DC fast charging. (When asked, a Kia representative said this was based on research, not experience with its own EVs.)
If correct, 10% might not sound like a lot, but remember that it would be on top of normal capacity loss and also combine with any range decreases from weather extremes or other factors. Add 10% to 20% then throw in some cold weather, and before you know it, your EV’s range is 30% of what it was when you purchased it eight years earlier — at least temporarily.
How to Preserve Your EV’s Battery Capacity and Range
There are things an owner can do to help preserve an EV’s battery capacity, and fortunately today’s EVs are designed to do some of these things automatically and to facilitate others.
Don’t Fully Charge or Discharge
The key to long battery life is not to use its full capacity, at least not all the time. Vehicles already do some of this themselves, which is why you might find two capacity specifications, in kilowatt-hours, for the same battery pack — such as gross and net or nominal and usable, where the first number is higher. The automaker maintains a buffer to ensure longer life and as a hedge against range loss. What you can do as an owner is not run your battery below a 10% state of charge unless you have to and not charge above 80 or 90% on a regular basis. Most EVs let you set a level at which the car will stop charging for this reason. For longer trips, you simply override the limit and charge fully.
Keep It Cool
You might not have a choice about where you live and drive, but you can choose where to park, and it’s best to park an EV in the shade or in a cooled garage when one’s available. Regardless of where you park, keeping the vehicle plugged in ensures that it can cool itself if necessary (most models), under the most extreme conditions, using grid power. There are other reasons …
Keep It Plugged In
As noted above, keeping an EV plugged in doesn’t have to mean charging it to 100%. It does allow the vehicle (depending on the model) to protect its battery from excessive heat or cold and precondition the cabin for comfort without compromising range. It also prevents deep discharging from lack of use, which can be more damaging to battery life than routinely driving it empty before recharging. The mysterious disproportionate loss of range in EVs that appear to be relatively new and/or have low odometer readings is usually associated with sitting discharged for weeks on end, perhaps repeatedly. The EV revolution has turned used-car buying on its head because what looks like a peach on paper (a few years old with very low miles) could be one if it’s a conventional vehicle, but if it’s an EV, it might be a dud.
Use It
An extension of previous warnings about not letting an EV’s battery discharge, it appears there’s no downside to working an EV hard. Geotab reports that using an electric car daily to the extent of its abilities — so long as you’re not resorting to damaging behaviors in order to do so, such as frequent DC fast charging — hasn’t resulted in accelerated battery degradation. Yes, the miles and charging and discharging all count, but there’s no additional penalty associated with frequent use.
Don’t Shop by Kilowatt-Hours
For the same reason we’d warn against buying one SUV because it has slightly more horsepower or a larger gas tank than another model, we warn against comparing battery kilowatt-hour specifications between models. There are so many other variables — such as weight, efficiency and aerodynamics — that these specifications alone don’t mean what they might appear to. The first SUV might not be quicker if it’s heavier, and the one with the larger tank might not go farther between fill-ups if it’s less efficient. The battery specification example is the same story, with one possible exception: when comparing different versions of the same model as opposed to a Ford versus a Tesla.
If a manufacturer has a smaller and larger capacity battery pack available for the same EV, then those differences should be meaningful. The “larger” battery is almost certainly heavier, but you can bet the automaker accounted for that or the upgrade wouldn’t do much good.
When choosing an EV, and especially when comparing different models, always use bottom-line specifications. For acceleration, look for 0-60 mph times, not the kilowatt (or horsepower) ratings of the motors. Range is tricky, but always start with EPA-estimated figures rather than making assumptions based on the kWh ratings of two vehicles’ batteries.
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