All the Things That Drain Your EV Battery

For context, this scale is bookended by the Lightyear One (104 Wh/km) and Tesla Model 3 (151 Wh/km) and, at the other end of the spectrum, electric minivans like the Mercedes EQV 300 Long (295 Wh/km).

“An electric vehicle’s main secondary energy use by far is to heat the cabin and battery,” says Matthias Tonn, chief program engineer for the Ford Mustang Mach-E. 

“When you compare an ICE to an EV, secondary systems become more dominant,” says Clemént Heinen, attribute lead in Polestar’s vehicle development team. “Whereas an electric car is driven by an efficient motor and battery pack, ICE cars use otherwise wasted heat generated by the engine to warm the cabin. The effects of those other elements, like the climate system, become very visible.”

Bishop’s calculations take into account a circulation fan; heating and cooling systems; heated front and rear screens; and heated mirrors, seats, and steering wheel. Heating and cooling systems are by far the largest drains of power in this category, requiring up to 3 kW and 4 kW, respectively, and robbing between 8.3 km and 11.1 km of range per hour of use.

Interestingly, heated seats are a far more efficient way to warm a car’s occupants, consuming 50 watt-hours each, taking just 560 meters of range per hour of use.

Lighting, electric car owners will be pleased to hear, consumes very little power. Bishop’s calculations estimate that a vehicle’s entire exterior lighting system, when used in a typical manner, accounts for 48.80 watt-hours (Wh) of energy. For a vehicle with an energy consumption of 180 Wh/km, which includes EVs such as the Porsche Taycan 4S, Tesla Model Y Performance, Kia EV6 Long Range, and Volkswagen ID.4, this equates to 0.27 km/h—or just 270 meters of range per hour of driving.

Car infotainment displays have grown significantly in the past decade, to the point that some span the entire width of the cabin. And some cars, like the Porsche Taycan, can be bought with up to five digital displays. The latest generation of Tesla Model S and Model X cars also come equipped with powerful video game systems, boasting 10 teraflops of power, roughly equal to a PlayStation 5, which has an output of 350 watts.

All of this draws significantly more energy from the car’s battery pack than the simple music and navigation systems of just a few years ago. While a regular car stereo played loudly might reach 100 watts of power, its demands on the battery pack are tiny, with 100 watt-hours equating to approximately 0.5 km of vehicle range per hour of use.

At this point, it is worth addressing how premium sound systems with huge maximum power outputs don’t necessarily drain an EV battery more quickly than a regular stereo. According to Bishop, while it’s possible to buy cars with sound systems boasting more than 2,000 watts of peak output, such huge amounts of audio power—2 kW—in practical use have little effect on battery drain. Here it’s important to remember how peak output is often only reached for a matter of milliseconds, and it is the ability to do that, even for just a thousandth of a second, that contributes to the better sound of a more expensive audio system.

Additionally, it is useful to know that powerful sound systems make use of capacitors to regulate their electrical demands. These are trickle-charged by the vehicle and then used to give the system a quick jolt of electricity when extra power is needed—such as when reaching that headline 2,200-watt for a millisecond.

USB ports are commonplace on most modern cars, often with a pair in the front and a further two or even three for rear passengers. We suggested earlier the possibility of removing an iPad from charge to preserve range, but there’s really no need. According to Silver Power Systems’ calculations, a regular car USB port is responsible for just 9 meters of range per hour of use. That’s about the same as using a windscreen wiper to clear a 15-minute rainstorm.

Secondary vehicle systems aren’t limited to those found in the cabin. The ABS, brake servo, power steering motor, and suspension compressor of many modern cars use electricity, but only a small amount. Broadly speaking, all of these combined account for about 100 watt-hours of power consumption, leading to approximately half a kilometer of range per hour.

“At highway speed, by far the biggest [energy] loss is aerodynamic drag,” says Fry. “For a Tesla Model 3, which has a drag coefficient of 0.23 and 2.22 m² frontal area, 9.5 kW of power is required to overcome aerodynamic drag. If we also consider a few hundred watts for tire friction, an estimated 90 percent combined efficiency of the inverter and motor, and another few hundred watts for the essential onboard computers, we need 11 kW to cruise at 70 mph.”

What if the car were driven slightly slower? Fry says by turning the cruise control down just 2 mph, to 68 mph, “drag power would reduce by 800 watts to 8.7 kW”—in other words, an 8.4 percent savings in energy consumption for a 2.6 percent reduction in speed.

Adding passengers and luggage can affect the consumption of an electric car. But, unlike an ICE vehicle, the regenerative braking system of an EV helps undo some of the energy losses experienced when lugging around more weight. Those extra kilograms increase the mass and momentum of the vehicle, boosting the amount of energy recovered back into the battery when coasting and braking.

“The number of passengers and luggage will change the energy required to bring the vehicle up to speed,” says Fry. “But it is not reflected in our simple 70 mph cruise example [outlined above], except for a small change in tire friction.”

Although they can’t be switched off to save range, like air conditioning, tires play a key role in the efficiency of an electric vehicle. Gunnlaugur Erlendsson, founder of startup tire producer ENSO, says: “If you put a poor set of tires on the car, it will dramatically affect the range.”

His thoughts are shared by Ian Coke, chief technical officer of Pirelli North America, who says that in the EV market, when you’re not using the correct tire you’re more likely to notice a loss in range and an increase in noise and other characteristics, “which will be exaggerated due to the powertrain.”

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