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Why charging speed is as important as range for owners of electric cars

In the electric car cosmos, maximum driving range is the number most commonly celebrated and debated. It’s a straightforward way to compare a battery-powered car with a similar gasoline-burning model — on paper, at least.

In application, gauging an electric vehicle’s daily usability requires factoring in things like its charging time and its charging capacity. Most modern electric cars have a range that exceeds a typical driver’s daily use. The question, then, is how quickly the car can get back on the road once it does run out of juice.

I sat spoke Audi’s engineers to learn what makes the difference between ordering a cup of coffee to go while you charge, and having time to wolf down a nine-course meal.

Miles versus kilowatt-hours

Audi E-Tron charging

The electric car lexicon is full of acronyms that are easier to make sense of than they seem. Kilowatt (kW) is a commonly used unit of power that, when we’re talking about charging stations, denotes how much electricity the charger dispenses. The higher the number, the more juice it can send to the battery pack. You’ll be back on the road quicker if you plug your car into a 150kW station than if you connect to one with a 50kW rating, or less.

Most EV owners charge at home or at work, where charging speeds matter less. If you get home at 6 pm and don’t leave again until 8 am the next day, your battery has time to leisurely sip electricity. If you’re making the 635-mile drive between San Francisco and Portland, however, odds are you want to be back on the road as quickly as possible, which requires taking into account the charger’s speed, and your car’s ability to handle it for an extended period of time.

Some cars reach their peak charging speed quickly, stay there briefly, and lose power to protect the battery, meaning they can’t take advantage of fast charging speeds. As a result, they need to spend more time plugged in.

Keeping cool

Audi E-Tron battery pack
Audi E-Tron battery pack

“Customers should not just be interested in the maximum value of charging power, but rather in how it progresses and may have to be reduced during a charging process, because otherwise, the batteries — for physical reasons — heat up,” explained Silvia Gramlich, the engineer who oversees charging time and charging efficiency development at Audi.

She cited the E-Tron as an example. It’s built on a 95kWh lithium-ion battery pack, though Audi capped its usable capacity at 86.5 to extend its life, and it can handle 150kW charging over a large portion of the charging process thanks to smart thermal management technology. It has 5.8 gallons of coolant traveling through about 130 feet of cooling lines to ensure that, under ideal conditions, the E-Tron’s battery charges at 150kW from 5% to 70% of its capacity. Its charging curve looks like the coffee table in your living room, not Pikes Peak.

In simpler terms, zapping the pack with 150kW unlocks about 68 miles of range in about 10 minutes, while an 80% charge can occur in about 30 minutes. The remaining 20% take much longer for technical reasons, according to Gramlich.

Throttling the charging process is necessary to ensure the battery holds a charge for as long as possible. We’ve all had phones that, as they aged, need two or three charges per day. Audi wants to ensure this doesn’t happen to its electric cars, which requires carefully balancing thermal management and fast-charging technology.

What’s next?

Audi E-Tron GT concept
Audi E-Tron GT concept

One of the biggest hurdles standing in front of the electric car is the time it takes to charge its battery, and some of the industry’s brightest minds are working on clearing it. Porsche’s Taycan is an excellent example. Released in 2019, the sedan is compatible with 350kW technology which makes the charging process (pardon the pun) lightning-quick. The company pledged that, again in ideal conditions, the Taycan can recover 60 miles of range in four minutes. Audi’s upcoming E-Tron GT, which will be based on the Taycan, should offer similar technology.

There’s a catch. Achieving these jaw-dropping numbers requires a charging station that can dispense 350 kW of energy. They’re becoming increasingly common on both sides of the pond, but you won’t find one on every street corner — not yet.

Until then, if you’re shopping for an electric car, remember to ask “how quickly?” after you’re handed an answer to the inevitable “how far?” question. You’ll thank yourself the next time you take a road trip.

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