If one measure can make or break the viability of certain cars, it would be the city and highway fuel economy numbers given to them by the Environmental Protection Agency (EPA), as buyers looking to save a few more bucks on fuel costs could simply look for higher numbers.
These numbers have benefitted bestselling compact gas-powered cars like the Honda Civic and Toyota Corolla and even hybrid vehicles like the Toyota Prius, whose latest model can achieve up to an EPA-estimated 57 miles per gallon in the city and 56 miles on the highway.
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With the advent of electric vehicles, things are different. Without any gas engine to account for, regulatory agencies have to figure out new ways to see how far they go on a full charge.
However, Stanford researchers claim that the EPA has it all wrong and that the general public is being lied to about the real potential of the batteries fitted to their EVs.
EV and gas car testing aren't apples-to-apples, says Stanford researchers
In a new study released by the SLAC-Stanford Battery Center, Stanford researchers and scientists suggested that the EPA's current methodology for testing EV battery range and degradation is flawed.
According to the EPA, the test it uses to project EV range doesn’t vary much from how it tests fuel economy in gas-powered vehicles. These tests are usually in a controlled laboratory setting, where a dynamometer (or 'dyno,' for short; essentially a 'treadmill for vehicles') is used to run a certain vehicle's gas tanks or batteries until empty.
But while the EPA will use dynamic testing variables such as turning on the A/C, driving aggressively, or running in extremely hot/cold temperatures to measure fuel economy in gas cars; the same consideration is not given to EVs, which the Stanford researchers see an issue with.
"We’ve not been testing EV batteries the right way," Stanford associate professor Simona Onori told the Stanford Report. Onori is one of the three lead authors of the study.
“To our surprise, real driving with frequent acceleration, braking that charges the batteries a bit, stopping to pop into a store, and letting the batteries rest for hours at a time, helps batteries last longer than we had thought based on industry standard lab tests.”
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As per the researchers, these "normal" driving habits that were once thought to negatively affect the life of EV batteries result in battery life, on average, lasting up to 38% longer than what is anticipated, or up to 195,000 miles.
According to the most recent data from the Federal Highway Administration, the average American driver traveled an average of 14,489 miles in 2022; with this average in mind, the average EV battery can last about 13-1/2 years under "normal" driving conditions.
The Stanford researchers gathered their data by designing four EV discharge profiles that would simulate a constant discharge to ones that replicate "dynamic" discharging based off real-life driving data. The team tested 92 different lithium-ion batteries for more than two years using these profiles and found that the more "lifelike" simulations resulted in higher life expectancy.
Hard acceleration helps battery aging
Stanford PhD student Alexis Geslin, one of three lead authors of the study, noted that once-held taboos like constant hard acceleration being bad for EVs is simply not true, noting that the study showed that being a bit heavy with the accelerator pedal helped slow down the battery aging process.
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The researchers say this phenomenon occurs because EV batteries age in different ways: aging caused by charge-discharge cycles and aging due to time.
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We all know that batteries left waiting to be used in a remote control, toys, and other gadgets, degrade over time when they are not used in said gadgets. However, it was always assumed that constant use of an EV battery would degrade the battery over time, however, Geslin reasons that it is not the case.
"We battery engineers have assumed that cycle aging is much more important than time-induced aging. That’s mostly true for commercial EVs like buses and delivery vans that are almost always either in use or being recharged," said Geslin.
"For consumers using their EVs to get to work, pick up their kids, go to the grocery store, but mostly not using them or even charging them, time becomes the predominant cause of aging over cycling."
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