Why DC Fast Charging Reduces EV Battery Life

March 5, 2022

The Different Levels of EV Chargers

Some EV automakers offer disclaimers on their websites to the effect that, “Frequent use of DC Fast Charging can have a negative impact on battery life and may limit battery performance over time.” Can DC Fast Charging harm your EV battery pack reducing range or durability? Let’s find out.

There are three levels of charging for today’s all-electric vehicles, Level 1, Level 2, and Level 3. Level 1 involves plugging your EV into a standard 120-volt receptacle that is found everywhere in your home and garage. It is the slowest way to charge your car, giving you 4 miles of range an hour. If you charge overnight, you’ll get about 50 miles of range for your next day of driving, which is actually more than enough for most American drivers. A full charge on Level 1 takes around 30 hours.

Level 2 charging is a bit faster, charging up to 30 miles per hour. It involves having your garage plumbed for a 240-volt receptacle by an electrician so that you can get a full charge in 8 to 10 hours depending on battery size. Every morning, you’ll wake up to the equivalent of a full tank. Besides being able to charge your vehicle completely each night, you’ll also find Level 2 charging available at many business locations, malls, and at free public charging stations.

To enjoy the benefits of Level 2 charging, you’ll have to purchase a Level 2 charger which will set you back around $700. With Level 1 or Level 2 charging, you’ll do most of your EV charging at home overnight when electrical rates are lower than during the day. You can also save money on installing a new 240-volt outlet by purchasing a Smart Splitter that can use the 240-volt outlet used by your clothes dryer. It automatically switches power to the device being used, so unless you like to dry your clothes all night, you can double up on your 240-volt availability.

How Does DC Fast Charging Work?

Level 3 charging is also known as DC Fast Charging and it utilizes up to 480-volts! You can find Level 3 chargers at over 40,000 commercial charging stations such as those provided by Electrify America or EVgo. While Level 1 and 2 use AC power to charge your EV through an on-board charger, DC Fast Charging, as the name implies, feeds straight DC power and can charge your EV to 80 percent in just 30 minutes depending on the vehicle and the outside temperature (cold weather makes batteries charge slower).

Because Level 3 charging can get you back on the road quickly, it is easy to see how you could travel across the country in your EV by “topping off” at these DC Fast Charging stations. The charging station monitors your car’s state of charge and only delivers the amount of power that your vehicle can handle. It regulates the flow of electricity so as not to overwhelm your charging system and damage the battery pack.

The flow of kilowatts increases as the battery warms up until it reaches an 80 percent charge. Then charging slows to Level 2 operation. This is called the DC Fast Charging Curve.

How Fast Charging Reduces EV Battery Capacity

The accepted wisdom in the EV auto industry is that faster charging will increase the rate at which an electric vehicle’s battery capacity will decline. Yet a recent study by the Idaho National Laboratory found that while an EV’s battery pack will deteriorate faster if its only power source is Level 3 charging, which is never the case in the real world, the difference is relatively small.

The Laboratory tested two pairs of Nissan Leaf EVs that were driven and charged twice a day. Two of the cars were recharged from Level 2 chargers, while the other two were on recharged at Level 3 charging stations. The EVs were driven on public roads around Phoenix, Arizona over the course of a year and the same set of drivers drove the four cars, testing the battery capacity at 10,000-mile intervals.

After 50,000 miles of testing, the cars that were charged using only Level 2 recharging lost around 23 percent of their battery capacity, while the Level 3 vehicles lost around 27 percent of their battery life. However, a big factor in this test was that the cars were driven in extremely hot Arizona weather during the summer and EV batteries do not like heat. The high heat of the area alone may have affected the test. While DC Charging may have had a negative effect on the test cars in question’s battery life, it was relatively minimal, especially when you realize that no one in the real world is going to only use DC Fast Charging exclusively to power an EV.

Limit Your DC Fast Charging

For the average EV owner today, 80 percent of all EV charging takes place at home or work using Level 1 or Level 2 charging. DC Fast Charging is generally thought to only be useful on road trips when you need a quick recharge to keep going on your extended journey.

Battery packs prefer comfortable temperatures just like we do. They work best at around 70 to 80 degrees. While fast charging delivers a lot of power, it can create heat which stresses out the battery more than AC charging. Heat stress has a minimal effect on batteries over time, but it is no doubt better for your EV to use Level 1 or Level 2 charging overnight to keep your car charged up. It’s cheaper, too.

Keep in mind that all EVs are not created equal. They have different battery voltage limits and different fast charging capacities. Each EV’s battery management system tells a DC Fast Charger how much power it can take at a given time. Level 3 chargers generally have a lot more charging capacity than a vehicle can possibly take and charging curves can vary based on the car, the charger itself, and the outside temperature.

The bottom line here is that most EV owners will find that they don’t use DC Fast Chargers all that often, but don’t be afraid to fast charge when the need arises.

Want to find out how many public charging stations are near you? Use our Charging Station Map right here on GreenCars.