Urban legends. Who knows how they start? One day you wake up to find everybody and their grandmother is saying if you use DC fast charging to put electrons back into the battery of your electric car on a regular basis, your battery will degrade faster and lead to an expensive battery replacement. It’s something a lot of people believe, but is it true?
Mark Twain once observed, “What you don’t know won’t hurt you near as much as what you do know that ’tain’t true.” That fits the electric car fast charging myth perfectly. The folks at Recurrent Auto are fascinated by EV batteries. They currently have over 12,000 subscribers who share their battery data with them.
One benefit of working with Recurrent is that when the time comes to move on from your current electric car, you will be able to get a report on the state of health of your car’s battery that you can share with potential buyers. The idea is to stop those in the market for a used electric car from worrying about whether they are buying a headache.
Recurrent says on its website, “Like your phone, EV batteries degrade over time. Factors like temperature, age, charging habits, driving style and battery chemistry all impact battery performance. Recurrent provides transparency so that you can have confidence in your electric car and its battery. When it’s time to sell, good batteries are worth more. EV owners in the U.S. can get premium offers from EV specialist buyers.”
In August, Recurrent published a new report about the relationship between DC fast charging and battery degradation. “We compared cars that fast charge at least 90% of the time to cars that fast charge less than 10% of the time. In other words, people who almost exclusively fast charge their car and people who very rarely fast charge. The results show no statistically significant difference in range degradation between Teslas that fast charge more than 90% of the time and those that fast charge less than 10% of the time,” Recurrent says.
The charts below show the rate of degradation to be virtually the same whether people use DC fast charging most of the time or hardly ever. The message here is: charge when you need to in any way that is convenient without worrying about the health of your battery. There may be factors that affect the rate of degradation, but how you charge your electric car is not one of them.
Initial analysis by the team at Recurrent suggests that the study findings can be applied across Tesla models and other EV manufacturers. Although, detailed research is being conducted on other popular vehicles that Recurrent supports. In short, the robust thermal, voltage, and battery management systems that EV makers have invested in do protect their batteries from damage with routine fast charger use.
Preserving Your Electric Car Battery
Okay, so now we know not to be afraid of DC fast charging if we own an electric car. Are there factors that do affect battery health that we should be aware of? The answer from Recurrent is: “Absolutely.” There are several times when fast charging may have a big impact on your EV battery, it says.
Avoid fast charging in extreme heat without preconditioning your battery. Preconditioning is when the car’s thermal management system pre-cools the battery so that it can accept a higher charge rate without overheating. Typically, if you set your car’s navigation to a fast charge station, the battery will be preconditioned when you arrive.
Similarly, precondition the battery before fast charging in extreme cold. Often, driving a bit before fast charging is enough to warm up the battery. In addition, avoid fast charging an electric car at very low states or very high states of charge, since battery resistance will be higher.
Recurrent emphasizes that almost all electric vehicles have software that will curtail fast charge speeds above 80% state of charge. In fact, it’s usually recommended to switch to a level 2 charger for the last 20%, as it may be as quick — or quicker. A level 2 charger, even a public one, is often cheaper, too.
The data used to prepare this latest report is confined mostly to Tesla owners. Different manufacturers use different batteries with different chemistries from different manufacturers. The only way to get reliable data for battery degradation over five years is to collect it over five years. No amount of computer simulations can substitute for real-world experience. One good way to get an idea of the health of the battery in an electric car is to become a Recurrent subscriber.
Charging speed is an area that confuses plenty of owners. We think because a DC fast charger says “250 kW” on the outside that our car can handle that much power. In each electric car model, software and battery limitations control how fast the car can charge. Charge speed is also dependent on temperature, state of charge, and even battery age.
If you drive a Chevy Bolt that is limited to 55 kW, plugging into a 250 kW fast charger won’t do you any good — and might annoy other drivers who could use that charger if you weren’t using it. Charging etiquette is something that is evolving, but being respectful of other drivers is always appreciated.
One thing to be aware of is that the cost of charging the battery in your electric car is likely to be far less if you are able to charge at home rather than at a public charger where rates of $0.45 per kWh are common. You can usually cut the cost of charging by half or even more by plugging in at home.
People who don’t drive an electric car always want to know how long it takes to charge one. That is a holdover from the days of gasoline engines. Who wants to hang around a gas pump any longer than necessary? But it ignores the one basic difference between an electric car and a conventional car. An EV can be plugged in any time it isn’t being driven. Whether it’s at home, at work, or at the grocery store, charging can happen at any time.
The typical private vehicle sits parked 95% of the time. Who cares if it’s plugged in when it isn’t being used? When people ask me how long it takes to charge my Tesla Model Y, I tell them, “One minute. 30 seconds to plug in and 30 seconds to unplug later.”* It’s all a matter of perspective. Unless you are taking a trip, charging times are largely irrelevant, so drive an electric car and be happy!
*Editor’s note: This is likely an overestimate. 30 seconds would be a long time for either plugging in or unplugging.
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