Will DC fast charging harm electric car batteries?

With electric vehicles hitting the streets and level 3 DC fast-charging stations getting ready to pop up along busy interstate corridors, readers wondered if frequent EV charging would reduce battery life span and void the warranty.

Liane Yvkoff
Liane Yvkoff is a freelance writer who blogs about cars for CNET Car Tech. E-mail Liane.
Liane Yvkoff
4 min read

I wrote a blog post a couple of weeks ago about a new charging technology by JFE Engineering that can charge a battery to 50 percent in 3 minutes, and up to 70 percent in 5 minutes. While the technology is impressive, some readers wondered if that fast-charging battery technology would have a negative effect on the life span on EV car batteries.

Well, readers have little to worry about since that technology probably isn't making it to the U.S. or in stateside electric vehicles any time soon.

There are few public level 3 charging stations in the U.S., and Ecotality, which is using part of its $114.8 million Department of Energy grant to build a network of fast-charging stations in five U.S. regions, won't begin installations until next year when electric cars start hitting the streets.

However, the San Francisco-based company has decided on a 60 kw power level for its charger and has equipped it with ports that comply with the Japanese Chademo level 3 charging standards, according to Don Karner, president of Ecotality North America. And even if Ecotality decides to add technology to its stations that would enable near instantaneous battery charging, no EVs in the U.S. market would be equipped to handle it.

"You can do it, but you will melt every wire that manufacturers use," said Mark Perry, Nissan director of product planning, "There is a DC fast charger that exists and manufacturers have agreed to."

Well, not all manufacturers.

Coda Automotive, an electric car start-up promoting a sedan with a 90-120 mile range, says its batteries currently handle only up to level 2 charging ports. It's waiting until the Society of Automotive Engineers (SAE) publishes its level 3 standard to make that option available on its sedan.

"We have a cell that's fast-charge capable," says Phil Gow, vice president of Battery Systems for Coda. The battery is charger agnostic, he says, but before the EV start-up decides to make level 3 charging available on the Coda sedan, it wants to wait for the SAE's standards to be in place.

Ecotality poised to roll out fast-charging EV infrastructure--photos

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The SAE has established a working committee to develop that standard, but no decisions have been announced or published. However, the Nissan Leaf supports DC fast charging and is compatible with chargers following the Chademo standard. Using Chademo compliant level 3 chargers, the Leaf can charge an empty battery up to 80 percent in 30 minutes. A battery only half empty can reach the 80 percent capacity in about 15 minutes.

That's a lot faster than the 12-15 mile range you get per hour of charging a Leaf using level 2 chargers, but it's not as fast as filling up a car with gas. But for the foreseeable future, it's as good as it's going to get.

"When you charge at five times the rate, you get 25 times the heating," explained Gow. And heat is the enemy of lithium ion batteries.

Coda's BMS has a 6.6 kw onboard charger--twice the size of the Leaf's--which provides 20 miles of range per hour of charging using a level 2 charger. While the Gow said that Coda is working toward supporting level 3 DC fast charging, he is "healthily skeptical" about the claims of superfast charging technology, such as JFE's, in just a few minutes. The electric vehicle veteran who worked on GM's EV1 battery warned that there are no shortcuts and no free rides when it comes to charging batteries.

Perry isn't saying that JFE's technology can't be used -- just that it's not going to happen within the next couple of years.

While SAE standards are still being developed for EVs, Coda is heavily investing in developing a battery and management system that will enable it to adapt to new standards and populate components as they are announced. Until then, they are focusing on developing a car with a range that meets the daily driving requirements for 90 percent of California's population--its initial market--without needing to refill until at night.

But let's just say that you live in an apartment building and don't have access to level 2 stations for overnight recharging, and you need to rely exclusively on level 3 DC fast chargers for power. Will frequent fast charging, if the EV supports it, affect the battery's lifespan?

Yes and no. Batteries are expected to lose capacity over time, and lithium ion car batteries are no different. However, thanks to advanced battery management systems (BMS) that carefully control temperature, they are leaps and bounds longer lasting than the mobile phone and laptop batteries that most consumers are used to.

The life expectancy of the Leaf's battery is about 70-80 percent of capacity after 10 years of normal use. Frequent fast chargers--more than once or twice per day--can expect performance on the lower end of that range, according to Perry.

The battery management system has built-in protection systems to prevent the user from doing any real damage. For example, if a user is trying to DC fast charge the battery for the third time that day, the BMS could automatically slow down the charge rate to 1.5 hours for an empty battery.

Annoying, but these fail-safe measures are better than voiding an expensive battery's warranty. Perry declined to say how much it would cost to replace a battery entirely.

Karner also believes that there shouldn't be a difference for customers who fast charge or use level 2 charging of batteries, although he hasn't seen the details of Nissan's battery warranty.

"We believe that DC fast charging is going to be an integral part of the infrastructure to support EV vehicles," says Karner. "Any credible EV manufacturer will want to support this to give customers full range of the vehicle to drive between cities and transportation corridors."