Electric Car Battery Life? – It’s not what you think…..
Photo: IEV-7S Courtesy JAC Motors China
In the first two articles, I wrote on the advancement of electric car technology I talked about how our understanding of driving in Bermuda changed after our family got our own electric car and some of the experiences we had and the questions that arose from our own family and friends. Things like the difficulty regarding how and when to charge and our notions about range. After that article, I ran into a few people who asked about some of the impacts of the technology, both good and not so good.
So in the second article, I discussed some of the misinformation out there about the idea of electric cars, why they are a paradigm shift and why it’s clear that as we move away from fossil fuel electric vehicles are the best future option and their numbers are only going to grow from this point forward. Today I’d like to go into some other myths we have about lithium-ion batteries and what most of us believe, and what the facts actually are.
As I’ve delved more and more into electric car technology in general and the battery technology, in particular, I am always surprised at the things I thought I knew as facts and just how misinformed I was about some things. Take for example a common misconception about EV batteries most of us believe that, like a phone or laptop, in a few years it will discharge so fast you will have to replace it. I understand that concern, I was one of the people with those types of concerns.
But the more reading I did the more I came to understand that even though cars and laptops use similar battery technology it’s not really an apples to apples comparison. I’m sure if you are like me when you first bought your latest smartphone, you probably, besides that guilty feeling of putting your old friend out to pasture, felt the relief of having a device that would actually survive all day without needing additional charging. Now fast forward a couple of years and you’re likely to run into the same scenario again, just as you did at the end of your last phone’s life: dead battery before dinnertime.
This is the crux of the issue that has influenced the way people view the lifespan of lithium-ion batteries and how individuals, new to electric vehicles, view them. The concern is if the lithium-ion battery in a phone can’t hold up, why should it hold up in a car?
Lithium-ion batteries are well-suited for use in electric vehicles for the same reason they’re well-suited to portable electronics like cell phones and laptops. They offer good energy density and are (relatively) lightweight – allowing for the maximum amount of range to be squeezed out of any battery being fit into a car. While the battery chemistry may be pretty much the same, the way the batteries are discharged and recharged makes a big difference in its lifespan.
….’it’s in the way that you use it’…..
My apologies to Eric Clapton for using his song lyrics, but battery longevity and performance are directly tied up in how it’s used. Cell phones have small batteries for their pocket-fitting form factor. However, In order to maximize the amount of time a cell phone can be powered on with such a small energy source, it’s necessary to allow consumers to use the entirety of the battery, from 100% all the way down to 0%. When a cell phone battery runs out of charge, it’s out of charge – there’s basically no energy left inside.
Recharging from 0% (or close to 0%) all the way up to 100% is the most intensive use-case for a lithium-ion battery. According to Isidor Buchmann, founder of Cadex Electronics and author of Battery University – a comprehensive educational source on battery technology – lithium-ion batteries can be cycled about 500 times like this before serious degradation begins to occur. That’s like almost 2 years at one cycle a day, sound familiar?
Just 500 cycles before obsolescence is perfectly fine for companies like Apple and Samsung, who would like you to buy a new phone every year, but two years of use doesn’t even come close to cutting it for cars, which are expected to last over a decade of use potentially by multiple owners. Thankfully, the batteries in electric vehicles aren’t put through these worst-case scenarios. They are in fact engineered to last many more cycles because of the serious protections in place designed and implemented to prevent them from dying early.
Battery Buffers ….Buffers the battery saver……
One of the most prevalent protection measures in use by most, if not all automotive battery industries, is referred to as a battery buffer. What this means is that essentially, a car driver is not able to use all of the electricity stored in their car’s battery pack. Even when the car shows you that there’s 0% energy remaining, there will actually be a buffer of electricity left in the battery to prevent that aforementioned 0% to 100% charge cycle that would accelerate battery degradation.
Courtesy Google Graphics.
While not all manufacturers publish the “usable” battery capacity for their cars, some actually have. Chevrolet did for the Volt plug-in hybrid. Chevrolet said of the Volts 18.4. KWh (kilowatt-hour) battery pack, only 14 kWh’s of electricity was actually available to drivers – or about 75% of the battery’s actual capacity. What this means is a charge of from 0% to 100% in the car is more akin to a real charge of from 15% to 90% – a much less intense use-case for the battery pack to accept. By structuring the battery pack in this way it allows for thousands of cycles before serious degradation starts to occur, instead of hundreds for a cell phone or laptop because of the much deeper cycles of charge and discharge. Furthermore, one of the worst things you can do to a lithium-ion battery is to run it down to 0% and let it sit empty without recharging it. This battery reserve is a way of preventing careless users from doing just that and ruining their cars because, again – 0% for the driver is not actually 0% in the battery.
Break it to make it….
Many of these ideas came about during the early days of Tesla as a result of lessons learned from the original Tesla Roadster. Back in those days, the Roadster didn’t have any reserve built into the battery. It was, therefore, possible to drain the battery to (literally) 0%. If the Roadster remains unplugged like that then eventually the battery pack would be compromised, and a new battery required to get the car in working order again. Remember all those stories about Roadsters leaving people stranded on the side of the road with no charge? While it was certainly possible back then to keep a Roadster battery in tip-top shape for many years of use, there wasn’t anything actually protecting the Roadster from the negligent use of its ownership, we hadn’t figured that out yet, Tesla was charting a new road and had to fail first in order to see what was broken.
Actual battery temperature management
After managing the charge cycle keeping the battery in its optimum temperature range was the most important aspect of increasing EV longevity and performance. This is known as thermal management. As it turns out Lithium-ion batteries seem happiest at about the same temperature as humans do: 70 degrees Fahrenheit. Coincidence…I think not, we are both made from a lot of the same chemicals, and the processes that take place inside us are affected by the external temperature just as batteries are.
While cold temperatures temporarily decrease range and performance, they don’t threaten battery life in the same way that really high temperatures say above 100 degrees F do. Operation at high temperatures for long periods of time can accelerate the speed of battery degradation. An EV’s ideal range would probably be between 50 and 90 degrees F.
To protect vehicles from suffering early range degradation, many (though not all) electric vehicles feature complex thermal management systems with liquid cooling to keep the batteries at a safe temperature. This makes a big difference for electric vehicles operated in especially hot climates, like Arizona or some Middle Eastern countries. Another consideration of battery thermal management is to account for high loads placed on the pack from active use like being driven for long periods at high speed.
Live long ….and prosper…
It’s no secret that electric vehicle batteries are expensive to replace, with costs often totaling thousands of dollars. While lithium-ion batteries may be newer automotive tech, cars have always carried something that cost big bucks to replace in case of failure: the internal combustion engine. Engines are expected to last the lifetime of the vehicle, even though their warranty period is usually around five years.
Electric vehicle technology is still relatively new, so it’s understandable that people are apprehensive – but the Tesla Model S, for example, has been out since 2012, the Roadster since 2008. Teslas’ have plenty of high mileage examples that have suffered only minimal degradation. We should expect the tech to only get better as we advance and get more data.
With EV batteries major manufacturers are now expecting them to last at least eight years and should in fact last even longer. I think we have reached a point where it’s best to think of them as lifetime components of the vehicle – they should essentially last for as long as the car does.
- Current Automotive;: Current Automotive was the first-ever, pre-owned electric vehicle retailer in the United States.
- EVANNEX, sells bespoke aftermarket gear for Tesla electric cars
- special thanks to Blane Erwin for his input to this article
- Also a shout out to Isidor Buchmann – of Cadex Electronics and author of Battery University