# Running on Empty: The Problem With Electric Car Fuel Gauges

Ford Focus EV - instrument panel

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Just a few months in and we’re already hearing stories of electric car owners getting stranded as their new electric cars ‘suddenly’ run out of power.

We’ve already examined the reasons behind why two 2011 Nissan Leaf drivers recently found themselves stranded without charge, but it got us thinking: do electric cars need to represent remaining fuel reserves differently?

Empty Really IS Empty

Unlike gasoline cars which inevitably have a spare gallon or two of fuel in the tank when the gauge shows empty, electric cars tend behave a little differently.

By the time most electric cars show an empty charge it is often miles away from running out of juice or entering a dangerously slow ‘limp home’ or ‘turtle’ mode.

Why Not Mimic a Reserve Tank?

2011 Nissan LEAF iPhone App

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To mimic the 20 to 30 mile reserve capacity of most gasoline cars, an electric vehicle would need to indicate an empty battery pack while it still had at least 5 kilowatt-hours of useable power left in the pack.

But to do that on a car like the 2011 Nissan Leaf, the car would need to show empty after only 79% of the battery had been used, resulting in reaching ‘empty’ after between 60 and 80 miles of driving.

Or in other words, going from ‘full’ to ‘empty in around 73 miles, the range estimated by the EPA as being the true range of the 2011 Leaf.

Inexact Science

Calculating remaining range on any car is difficult. Ten years ago, drivers only expected to know the amount of charge (or fuel) remaining. Now it’s expected to include a calculations indicating just how far the car can go before it reaches empty.

Based on past driving, these calculations can be wildly unrealistic.  Just a few months ago we drove a 2011 gasoline Volvo C30 120 miles and arrived with the on-board computer telling us we had more remaining range than we did when left.

In other words, smooth driving can reap rewards in range calculations. But a few spirited overtaking maneuvers and harsh driving can cause estimated range to drop like a stone in little more than a few miles.

State of Charge, not Range Calculation

2010 Tesla Roadster Sport 2.5 Cold Weather Testing

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An obvious solution to this would be to display the car’s state of charge rather than estimated range. In order to be useful however, the resolution of each segment of the display would have to be far greater than the current 10 or 16 segment displays used by most automakers.

The ultimate aid would be a digital display displaying state of charge as a percentage, as found in cars like the 2011 Tesla Roadster.  This enables drivers to see with much more clarity just how much charge they have remaining without inducing range anxiet

Better Software

Ultimately though, electric car manufacturers have to acknowledge that their cars will be driven by people who are used to the world of gasoline fuel gauges, in which range calculations are often underestimated rather than overestimated and there’s always reserve fuel at the end of the dial.

But while early adopters may be willing to relearn how to read how much fuel they have left, those who follow won’t, putting the onus on automakers to improve the accuracy of range reporting or suffer at the hands of a public transfixed with range anxiety.

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1. IMO it would be a really difficult psychological hurdle for a manufacturer to have a meter that read empty after 70 or 80 miles when the range is only expected to be 100 total miles on a good day.
It seems that it really is time to recharge if your EV has only 20 to 25 miles of range left. An ICE driver would be seriously anxious if the range read

2. well, the first real glitch for evs to overcome - accurate meters.
one of two things will occur - 1) they will get it fixed. 2) they will need to come out with battery ranges faster than they originally intended.
one way or the other, they will sell us the cars.
at this point, there is still a lot of room for others to jump in. including coda, if they can meet that august deadline, and their thermal battery mgmt system be more accurate.
i see this as all good for the consumer, in the long run.

3. The ultimate aid would be a digital display displaying state of charge as a percentage, as found in cars like the 2011 Tesla Roadster. This enables drivers to see with much more clarity just how much charge they have remaining without inducing range anxiety,
BINGO!
I really want to see how Mitsubishi handles this in their i-MiEV. If Mitsubishi production hasn't been screwed up by the quake/tsunami that is. Last I heard Mitsu is still online and on the way to producing fairly well their automobiles, perhaps a parts inavailability deal there or there. But I want to see if their method of showing battery "power" left is in this percentage display method like Tesla or not.

4. Good article and good suggestions. Hopefully, the manufacturers will read this and provide good information for drivers in the future.

5. This article points out the inherent flaw in any pure electric car. In my congested urban area (Chicago) any trip can take twice as long as expected if a blip in traffic occurs. I guess the Chevy Volt is the right design after all.

6. Notice how little they are pushing electrics? Where are all those ads? Much more profit in polluting cars.

7. It ist high Time that someone produces an emergency generator with Wankelmotor, it will weigh under 30 kg and gives 20 kw.
By sure distances leve it at home, save weight, in doubt take with you as rangeextender.
If you have enogh \$\$ buy an Volt.

8. Ingineris, an electric car actually has the advantage in that situation, as it uses no power when caught in traffic except lights/aircon. A Volt would be burning gas the entire time (if its generator was on).

9. Averill - The Volt's engine shuts down the same as a Prius at stops and slow acceleration so it will not be burning gas, as you say "the entire time".

10. After reading most of these so far.
I am glad I bought a Volt just three weeks ago. I just love it. And yesterday I drove it up to 51 miles before the gas generator kicked in. The range just seems to extend each day that I drive it after a full charge.

11. #10 Stan - Me too. #1756. My experience is very much like yours. I don't know it the car gets better as it goes along, or if we learn to drive better, LOL. Congratulations!

12. The Mitsubishi i MiEV does emulate a reserve tank. Once the gauge shows '0 MILES', you have around 4-5 miles before the 'Tortoise' light comes on. Then you've got a mile or two at reduced speed before the car comes to a halt.

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