Searching for a “Range Anxiety” Scapegoat
I wanted to blame Nissan. For all the glories of the Nissan LEAF—which I’ve been enamored with since making it my daily ride three weeks ago—the company made a fatal flaw in its dashboard display of existing range left in the all-electric car’s battery. That’s how I felt last week after what I had assumed would be a routine trip last week from Berkeley to see friends in San Francisco and nearby Daly City.
I backed out of the driveway in the morning with 102 miles of estimated range, according to the car’s computer estimates. The number of estimated miles, and twelve bars representing the level of state-of-charge, are the two pieces of information the Nissan LEAF provides drivers to indicate how far the fully charged 24 kWh battery can safely go until it needs to get plugged in again.
As we’ve discussed on this site, what EV drivers want most is a plain-and-simple percentage number for the State-of-Charge (SOC) of the battery. With a percentage number, and an awareness of past efficiency—probably about 3.3 or 3.4 miles per kilowatt-hour—you can get a decent idea of how much range is remaining.
Instead, the on-board computer takes a guess at remaining mileage. That number is simply too erratic to be useful. The number jumps up and down by five or 10 miles, depending on how you’re driving at the moment, if you have the AC on, or if you’re using Drive or Eco modes. The computer obviously doesn’t know if you’ll continue to drive in the same fashion, but it tries nonetheless to give you an approximation of the remaining range. It doesn’t take long behind the wheel of LEAF to stop putting much faith in that number, especially during the early part of a trip when there’s a lot of juice.
Driving by Numbers
So, I took off on the first leg of my trip, to downtown San Francisco, about 12 miles away, to meet a friend for a cup of coffee. No problem. Then, I traveled another 15 miles to Daly City, just south of San Francisco. I was keen to show off my LEAF to my pal, who is contemplating buying an electric car. He suggested a restaurant all the way back in downtown San Francisco—essentially doubling back another 15 miles. The ride back into town was a chance to demonstrate the LEAF’s quick acceleration in D mode, with the AC keeping us cool. All my attention was focused on the driving experience, and just 45 or so miles into trip, range was not on my mind.
Again, the fact that the estimated range showed 60 miles or 50 miles or whatever didn’t matter—because that number jumps all over the place. The last thing you want to do behind the wheel is to start tallying numbers. Besides, as soon as you slip into Eco mode and turn the air off, you get the indication that there’s plenty of juice left for the day of driving.
The 12 "state of charge" bars—while less erratic—also seem symbolic, because with about half of them left, I should have had about half the battery left. With an estimate of 90 or 100 miles at the beginning of the day (and a consistent driving style), I shouldn't be the least bit worried about range.
Things quickly changed. After lunch, we headed back to Daly City, which is moving in the opposite direction from home. I needed to get there and back home in about an hour to pick up my kids from school—as I had promised my wife I would. In the short time on the faster highway route back to Daly City—zooming along at about 65 mph along with the traffic—the symbolic nature of the estimated range and the twelve bars got extremely real, extremely fast.
By the time we reached his house, it took me by surprise that I was down to three bars and an estimated 15 miles of range for a 20-mile trip home (according to the nav system). How did it shift so fast? Was that a real number? Even though I was pretty sure the LEAF was underestimating the range left, I had no way to tell for sure. My only choice was to stop, take a trickle charge for at least an hour, and pick up another five (insurance) miles. I also had to call me wife to explain that she needed to interrupt her appointment to pick up the kids. The experience turned my range anxiety into the much more dangerous variety: marital anxiety.
An hour-and-a-half of 120-volt charging later, with 22 miles of estimate range and four bars, I prayed to the EV spirits and took off for home—with AC off and in Eco mode.
Then, the fortunes of battery state-of-charge changed again. After only a half-mile of slightly downhill driving to the highway, I was up to an estimated 26 miles of range. On the steady ride home through congested rush-hour traffic, that number barely budged—and only until the last three miles of the 20 mile journey did it drop down to 16 miles and three bars.
What?! If I really only had 22 miles, I should have been down to a single bar and two or three miles of range left—but I still at 16 and three bars. What was underestimated back in Daly City was now either accurate or overestimated—but regardless, the dashboard information only served to induce range anxiety, instead of dispelling it.
Who’s to Blame?
I still want to bust Nissan’s chops for not providing that SOC meter in a single percentage number. C’mon, why not trust me with that number? But after further study, I don’t think it’s so simple. After speaking with a few battery experts, I now know that it’s tricky to measure SOC. It’s not like putting a gauge on gasoline sloshing around a gas tank. Any number of factors makes it difficult to know for sure how many miles or real-world miles are left for a driver. Maybe Nissan was watching my back, by compelling me to charge up a bit, to prevent me from getting stuck on the roadside.
My best guess is that I never really needed to stop to plug in before taking off on the trip back home. I’m almost positive that I could have picked up the kids as I promised. The problem wasn’t that the 24 kWh pack lacked sufficient range for my day of driving. It was a measurement and communication problem.
There's a tremendous national effort underway to extend the capabilities of today’s battery technology. Now, I’m wondering if a big chunk of those resources should be put into better systems for letting drivers (and their spouses) know what’s already there and waiting to be used. There's no sense in blaming the car companies, the battery technology, or the driver for a lack-of-range problem that might not exist in the first place.
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