Op-Ed: Time for a New Metric Instead Of MPGe?

MAR 17 2014 BY DSCHURIG 82

The Nissan LEAF Is Rated By The EPA At 114 MPGe Combined (Shown above in "Autonomous Drive" Version at the 2014 Geneva Motor Show)

The Nissan LEAF Is Rated By The EPA At 114 MPGe Combined (Shown above in “Autonomous Drive” Version at the 2014 Geneva Motor Show)

EV’s are a new technology. Well, actually not that new at all, but newly on the rise. As we continue to adopt them at ever increasing rates, we are in need of a new way to relate their performance to our familiar form of transportation as a point of reference to understand their benefits.

The EPA developed the metric Miles Per Gallon Equivalent – MPGe. It is a simple conversion using the energy density of gasoline in kWh equivalence. But what does it mean? EVs don’t use gallons at all so it is a totally contrived metric that doesn’t give us any kind of feeling about how EVs really stack up to ICEs because the two fuels have dramatically different costs. It really isn’t that useful.

It’s great that there is some kind of equivalence to gallons but what we really want to know most often is what does it cost to drive one vs. the other. That is the first question out of all of my friend’s and colleague’s mouths, “What is the savings on fuel?” 聽They definitely do not know or care about MPGe. It is somewhat useful for hybrids to measure their performance since they use multiple fuels I guess but it ends there.

2014 MPGe Ratings Of A Few Popular EVs

2014 MPGe Ratings Of A Few Popular EVs

We need a new metric that is normalized to the basis that we most care about and have the most connection to – dollars. One such metric could be Miles Per Dollar, MPD – how many miles can we drive for one dollar. It is simple really, it is just a matter of taking the mileage of an EV divided by the cost of fuel for the EV. Likewise for an ICE, it is the mileage of the vehicle times the cost of fuel for the vehicle.

Analogous to the Consumer Price Index (CPI) which is the cost for a standard basket of goods, call the cost of electrical fuel (electricity) in dollars per unit the Electricity Price Index, EPI, and call the cost of gas fuel (gasoline) in dollars per unit the Gasoline Price Index, GPI. Then:

MPD Calculations

MPD Calculations

Very straight forward as long as the EPI and GPI are constant, what do we do about the fact that prices change daily for both gasoline and electricity? The two indices will be all over the place and MPD will change from day to day. But how much do they really change? Here are the prices for each charted over the last two years as reported on ycharts.com:

US Average Retail Price of Electricity (ycharts)

US Average Retail Price of Electricity (ycharts)

US Average Retail Price of Gasoline (ycharts)

US Average Retail Price of Gasoline (ycharts)

If we look at prices for each over the last two years, they really haven’t changed that much, generally within 5% of their average over that span. There are seasonal changes but on the average they have not increased at all, not even in keeping with the CPI. Gasoline is actually trending down slightly over the interval.

That being said, for the sake of this metric of comparison we can say they are constant and equal to their average, EPI = $.0997 ~ $.10 and GPI = $3.66. From the formulas above simply divide your EV mileage by .1 and your ICE mileage by 3.66. What you get is a very simple, practical and real world evaluation of marginal cost performance. Of course it does not account for maintenance, tires, registration or insurance but it is representative of the large majority of the cost of personal transportation. For example:

For a Nissan Leaf
3.4/.10 = 34.0 miles/$ = 34.0 MPD

For my Kia Sportage
28.0/3.66 = 7.65 miles/$ = 7.65 MPD

So I get a little over seven and a half miles per dollar from my current ICE whereas I would get thirty four miles for that same dollar in a Leaf. For my friends and colleagues, I would get over twenty six more miles per dollar driving a Leaf instead of my Kia. To get savings between the two vehicles for a given commute, simply divide the commute distance by MPD to get cost for each and compare. Much easier to understand.

Then we assess the EPI and GPI cost indices periodically, as we do with the CPI, and update them as necessary, perhaps annually. What do you think?

Categories: General

Tags:

Leave a Reply

82 Comments on "Op-Ed: Time for a New Metric Instead Of MPGe?"

newest oldest most voted

MPD is cute but it varies, not just in time but also locally and depending on tariff plan at home,tariff plan for using charging infrastructure, use of solar etc so a lot of variables need to be accounted for to get any meaningful results. Not a particularly practical measure.

Wh/mile or KWh/100 miles is the only measure for EVs that make sense though of course only useful for comparing EVs with other EVs, not for comparison with ICEs.

I’m with you; no MPD. The one thing you COULD do is something similar to what they do on large appliances. You have that yellow energy efficiency sticker with an arrow pointed to “estimated yearly cost to run this appliance.” But don’t use that to replace MPGe, just supplement it. And you can have an estimated cost to run this car for a year, 12,000 miles per year, and an arrow pointing to a cost (like the appliances) and another arrow pointing to the equivalent car of the same size/class. Then, of course, note that you’re assuming $0.12/kWh, $3.50/gal gas or whatever. And if you could sneak in oil changes to that estimate…

I think it’s a poor choice to tie it to something as fluid as dollars and commodity prices. It is also tough because fuel and electricity price vary so much per location. It also doesn’t help with phevs and their blended range vs current mpge.

I think this method would lend itself well to an app or calculator to compare total cost of ownership of various vehicle choices. This is not something I want the fed to start doing.

I hope someone start using miles per kW. If you know how much you pay for electricity its easy to take that number and turn it in to miles per dollar.
I think that people who are shopping for an EV want to compare EVs with EVs. They already know that EVs har much cheaper to run than gasoline/diesel.

+1
Electricity is measured in KW/h. So it must be miles per KW/h or KW/h per 100km (in Europe)

The EPA did extensive studies on this in the United States, with study groups, consumer surveys, etc, when they were creating new window stickers for electric vehicles.

Not only did they find that US consumers overwhelmingly did not know what kw’s and kwh’s were, they overwhelmingly DID NOT WANT TO LEARN what they were! Shocking, I know…

Sadly, it does not matter what is the scientifically best metric to measure electricity consumption in EV’s. What matters is what can be dumbed down enough to be understood by the general US consumer. Don’t believe me? Look back 40-50 years to the adoption of the metric system in the United States….

I concur. Miles per KW/h or KW/h per 100km is the best.

Folks! If you are going to be discussing energy usage or energy storage be advised that energy (for EV purposes) is measured/quoted as follows:

Not in kilowatts (kW)
Not in kilowatts per hour (kW/h)
But in kilowatt hours (kWh)

Abbreviating kWh to kW confuses everyone and makes the writer seem ignorant.
Using kW/h removes all doubt.

Sorry, but somebody had to say it!

p.s. kW is a measure of power, not energy.
Power is the rate of transfer of energy and is analogous to horsepower. In fact 1kW ~ 1.3HP.
Harrumpfff!

+1

You’re my hero MikeM.

It’s too bad people in general aren’t more science-literate. If they were, these relatively simple concepts wouldn’t be so difficult to understand.

+1, except you contradict yourself mid-way through (typo?), and… the correct way to write kilowatt-hour is actually

kW路h

with a multiplication middle dot aka interpunct between kW and h. Or if that symbol isn’t handy, kW*h

Now if we wanted it to be all nice and clean, we’d speak of energy in its proper SI unit, in watt-second (not hour), aka the JOULE.

My vote for EV economy/consumption would be for (kilo)joule per meter, or (k)J/m.

People are already unable to accurately compute cost per distance without some kind of calculator or app, so why not pick up proper units for new vehicles at least?

But yeah, trying to get more Americans familiar with the infinitely more sensible units system used everywhere else (except maybe Burma) will probably prove even harder than convincing them that not all vehicles have to burn gas…

kWh is a standard abbreviation.

I don’t think most people in the USA know what Joules are. My electric meter only shows kWh, and my electric bill only shows cost/kWh. So throwing Joules into the mix would just add to the confusion, at least here in the USA. Sure it could be taught, but our government-run (aka “public”) schools have higher priority subjects like this:

http://answers.yahoo.com/question/index?qid=20081216213537AAHTyf3

I knew a guy named Joules once.

Just because some lack education is not an excuse to make the system stupid for everybody.

MPG is ok for gas cars but dumb for EVs. Using kW路h would be just the opposite.
And neither make any sense for CNG or FCVs.

It’s really time for Americans to join the other 96% of people who use non-f*d-up units.

I addressed all this in more details here: http://insideevs.com/op-ed-time-new-metric/#comment-403400

@Jonas

Agreed. miles/kwh makes the most sense.

I disagree because MP KWH runs a tight range to ~3, where electric prices are the economically compelling variable. You actually need both, but its the electric price per mile that is most compelling.

EPA sticker already provide kwh per 100 miles. So, this amounts to a format change, where the electric price assumption (12c) can be wildly off. They made the more-variable variable static, and the less-variable variable dynamic. Follow?

No, but I think that’s exactly your point 馃檪

I agree … miles/kWH is the way to go because it mimics the MPG metric people are already used to. For consistency with MPG, I would abbreviate it MPK. A plugin hybrid like my Volt would have both ratings. Maybe something like this:

45 MPG City, 35 MPG Highway
4.2 MPK City, 3.4 MPK Highway

This is so simple and it works for gas cars, hybrids, plugins, and EVs. Buyer just has to know… bigger numbers are better.

Only government could hatch a metric as confusing as MPGe.

The price of gas also includes substantial taxes to pay for roads.

The cost of those taxes should be stripped out because eventually EVs will be taxed for their use of roads either by a yearly fee (like some states) or some other mechanism.

What do you mean by “substantial”? I thought the gas taxes were low.

By simply using kWh/km (kWh/mile in us) we ceep it clear. It will work globaly aswell, just plot your prise per kWh and you have it. then we dont need spesific standards for diferent countries or regions.
I find, sometimes ading more standards to simplify will just complicate matters.
(But maybe i am wrong)

It should be miles per kilowatt hour, or mpkw for short, since we already measure the size of an evs engine by how kilowatts it can put out as in the 2 choices for battery packs that the Tesla Model S has, an 85 kwh choice and a 90 kwh choice. That makes the most sense because of the type of energy spent by the car per mile of driving just as mpg makes since for a gas powered car because it will spend a certain amount of gallons of fuel per mile of driving.

While I understand and appreciate the desire for a metric that gives an easy cost comparison for different vehicles, I have some problems with your proposal. I live on an island where the exchange rate of the local currency can change a lot resulting in significant changes in the prices of both gasoline and electricity, which in our case is still largely generated with oil fueled generators. For example between 2012 and now the amount of local currency required to bu a US dollar has gone from 86 to 108. There is also tremendous pressure on our politicians to try and come up with policies that will reduce the cost of electricity from it’s current 42 cents per kWh, with a 30% reduction over the next couple of years being promised with the introduction of some gas fired generators. So the local effect could be electricity prices going down at the same time fuel prices are doing up. When you consider the different scenarios in different countries all over the world, this has the potential to be even more confusing than the different fuel efficiency metrics of litres per 100km in Europe vs mpg in the US. One thing about… Read more »

Puerto Rico is going with natural gas, and I don’t think they have LNG offloading capacity. Otherwise, diesel=islands and that’s expensive. On the bright side, think of how much faster grid parity will come to you.

Even if prices vary, using it is obviously the best way because in the end, that is what matters to people.

What counts is cost.

My critisism is only this:
it should not be ‘miles per dollar’, but ‘dollars per mile’.

What matters to people is not how much they get for their money, but how much money what they want to get will cost them.

Obvious example:
At the gas station you do not see how many gallons you get for a dollar, but how many dollars a gallon will cost you.
Based on your car, this translates to how much will each mile of driving put you out of pocket.

dpm ev vs. dpm ice

This means for a given monthy/yearly distance travelled:
driving cost ev vs. driving cost ice

We definitely need some sort of number. Heck, Compact Fluorescent bulbs are still marketed by their equivalent light output in WATTS.. So you see a 13 Watt bulb marketed as “60” despite having a much better metric for measuring that, such as lumens.

Unfortunately, the cost of gas varies, as does the cost of electricity, and the value of the dollar. So I can’t come up with anything that doesn’t depend on at least one of those.

A better equivalency spec that light bulbs should prominently advertise is lumens.

light bulbs also carry a lumens label. I like having both — the “w” tells me which bulbs to start looking at, since I haven’t learned how to read lumens, yet. Then the lumens tells me which of those bulbs is brightest. I’m excited that we are transitioning to lumens, and happy to have the safety wheels of “W” for a while, too.

M/kWh, measured from the wall.

The cost could be zero, from free EVSE or made at home by solar. Try that with gas.

“The metric system is the tool of the devil! My car gets forty rods to the hogs head.. and that’s the way I like it!” – Grandpa Simpson

+3

I agree with the other commenters but offer this suggestion. Why not build a little smartphone app (maybe even linked with an app like gas buddy) that allows every individual now matter where they live to compute MPD based on their real-world data. We could continue to base fleet-level comparisons on kWh, but individuals could translate that to something more useful when asked by their friends “how much would your EV save me?”

+1 on MPGe being dead on arrival. I’ve ranted on EPA’s selection of 12 cents being an average electric rate, too, as they simply average the 50 states (HI @~$.30 and TX @~$.09) rather than divide US residential dollars spent, by total kwh. TX consumes 10x as much as HI. If done this way, 2012 was about $.097/kwh.

2 more things:

1 – “Cents per mile” already exists, as compensation for using a car for work. It’s portable across other energy forms and to the OP’s point, it’s economic

2 – As mentioned, gas is about the same price everywhere relative to electricity prices, which are all over the map in comparison.

Monroney window stickers should drop MPGe and eGallon, and begin to make local representations of KWH cost, whether state average or something more local. The EPA does have a calculator that helps evaluate the $$ behind kwh storage in PHEV:
http://www.fueleconomy.gov/feg/Find.do?action=phev1Prompt

Whatever you do, just make sure to put distance driven on the denominator. I don’t know anybody that sets aside a budget for driving, or buys XX gallons of gas in a year and then drives as far as they can on that amount. Most people drive XX miles per year and spend whatever it takes to accomplish that. Sure it’s the same thing either way, but XX/mile or XX/100 miles or XX/100km just makes it easier for people to put things in perspective and make more appropriate comparisons.

See kdawg’s post about grandpa Simpson above.

I agree, a consumption metric is preferable over an efficiency one.

+1
I realize many Americans want to fight metric to their death, but it really is a better and easier system if you take a minute to actually learn how it works.

Look at current fuel ratings (won’t even touch on the different definitions of a gallon in different regions, that’s a whole other story):
MPG: The higher the value, the LESS fuel and the LESS cost (exact opposite of what you would think when looking for efficiency. Right away there wasa higher learning curve on this one when you first learned it!)
And the higher you get in MPG, the less beneficial a fixed drop is. I.e. 35->40MPG is essentially nothing compared to 10->15 MPG, despite both being a 5 MPG difference.

Now look at L/100km (or kWh/km [miles, if you insist]):
A lower number means LESS fuel used and LESS cost. Amazing, a number in which all components agree! So difficult to understand, this metric/SI.
And it is a linear scale. If you reduce 1L/100km from any point in the scale, its the same. 10->9 or 2->1, the net savings is the same, as expected by a net change of the same L/100km.

I like the idea of just using a neutral international standard unit of energy like the megajoule. So if your EV gets 3.5 miles per kwh that would come out to about .29 kwh per mile or a nice 1 MJ/mile. An ICE car with 35 mpg would come out to about .029 gallons per mile or 3.82 MJ/mile. Nice small easy to understand numbers. One wouldn’t have to know exactly how many miles per dollar this way because 1 MJ worth of gasoline (1 MJ = .0076 gallons) is .0076 gallons x $3.66 per gallon = $.0278/MJ. Which is very close to 1 MJ of electricity (1 MJ =.2777 kwh) .2777 kwh x $.0997 per kwh = $.0276/MJ. Right now they are surprisingly similar in cost per MJ but even if the price of each energy source fluctuates it doesn’t have a huge impact of the difference between ICE and EV cost per MJ. This works for quite a few countries with exceptions. For example, cents per MJ are out of balance quite a bit in Germany because of the huge renewable energy infrastructure projects they are paying for right now. But in France for example the cost per… Read more »

MJ – Michael Jackson? Michael Jordan? ;

What?! EVs run on millions-worth of jewelry?!? 馃槈

The issue here is too many unit conversions, many with variable rates. I mean, how do you really feel about BTUs and therms? 馃檪 What about calories vs. Calories?

Let’s not convert to yet other meaningless to most undereducated folks units.

Because kilowatt-hours is easy to understand? No, it doesn’t make sense to sophomore engineers, so for ordinary people it’s just a stupid wall to climb over.

Sophomore engineers should not have an issue integrating power over time. We are not talking about boiling water or thermodynamics, we are talking about electric power here produced by a battery with a certain voltage delivering certain current to the load (inverter).

No joules, no gallons, no dollars, no equivalents.

Wow, are you serious?? You call the joule an “equivalent”?
I thought that your post below about MJ meaning Michael Jackson was a joke, but apparently you’re indeed that “challenged”. Please reassure me: you’re American, right?

Let’s go back to your rant: “we are talking about electric power here produced by a battery with a certain voltage delivering certain current to the load”

So the best units for power and energy, respectively, would be the ones most accurately and directly reflecting that ‘certain voltage’, at a ‘certain current’, and (for energy) over a certain time, don’t you agree?

Power: 1 volt 路 1 ampere = 1 watt

Energy: 1 volt 路 1 ampere 路 1 second = 1 joule

Oh, btw, this works for power or energy from any source, not just electrical. Generalizing for anything capable of pushing a car:

Energy as force over distance: 1 newton 路 1 meter = 1 joule

Note how simple and elegant this is, how all the constants tying those units together are 1.

I now see that you posted another related comment below suggesting instead kW路h as unit of energy. I don’t think it makes much sense, and I’ll reply to it explaining why.

So just because some are undereducated (and if your message wasn’t sarcasm, including yourself), you’d suggest we stick to even dumber metrics, insulting everyone’s intelligence?

I’d argue quite the opposite actually: if supposedly educated people (e.g. at the EPA) were more consistent with units — including favoring the metric system, which is demonstrably far less confusing than the mess the US persists in — then maybe just maybe it’d get more people to understand how things work, and help with the current less-than-stellar average education level in the country.

The fact that a sizable fraction of the US population is effectively scientifically illiterate, and unable to understand any research done worldwide because it’s in an unfamiliar system of units, isn’t just a national embarrassment, but a terrible drag on the country’s competitiveness.

Dumber metrics is exactly my issue. Can we at least agree that MPGe has not helped to proliferate EVs?

MPGe is stupid, but I’d say this even if it somehow did contribute to make plug-ins popular. Measuring energy in gallons is dumb on so many levels…

Now vdiv, what was your beef with the joule and/or MJ (which is the correct abbreviation for mega-joule)?

You realize that the joule is the SI unit of energy, 1 watt 路 1 second, regardless of whether electrical, thermal or mechanical, don’t you?

The idea here is to communicate to the common man what the efficiency/consumption of this newfangled EV thing is. The way we identify electric consumption, even in countries that use the metric system, have a stronger secondary science education, and have a better chance of knowing what is a SI unit is kWh.

So you suggest measuring energy in kW路h instead, because that’s what many utilities still use for electricity. Converting to and from joules is easy (1 kW路h = 3.6 MJ), so for electricity, yeah, we could use either.

The problem is, if we go with kW路h for EVs, how would you suggest we compare their efficiency with gas, CNG or fuel-cell vehicles? Or even just put meaningful consumption numbers on plug-in hybrids?
Measure gasoline, hydrogen etc in kW路h too?
We’d be right back into the same kind of non-sense as measuring electricity in gallons in MPGe…

This is why, in my opinion, again, when it comes to comparing the energy consumption and/or efficiency of vehicles with different and/or hybrid drivetrains, possibly from different countries, the only units which make sense are the standard ones.
http://en.wikipedia.org/wiki/International_system_of_units#Units_and_prefixes

Thanks io you stated the argument perfectly.

I think comparing EVs and their energy consumption to fossil fuel vehicles misses the point of EVs and is detrimental to their adoption. Just consider all the talk about coal power and the long tailpipe. Even if EVs were less efficient than oil burners the fact that they can use renewable electricity at ever decreasing cost produced in so many ways makes them very important.

Let’s take this to its logical conclusion. The problem with the dollar is that it is not international currency. It has been previously proposed that an international exchange constant is a commodity that is sold everywhere on the planet. Thus, the BMI or Big Mac Index, a constant value unit based on the price of a Big Mac at Mcdonalds:

http://en.wikipedia.org/wiki/Big_Mac_Index

Thus we have Miles Per Big Mac or MPBM, trading at about $4.2 USD.

Miles per Bit Coin

Miles per bitcoin graph:

——\
\
\
|
|
|

Attempt to draw cliff function thwarted by web editor! Ratfish!

I vote miles per MegaJoule or MegaJoules per mile because it hangs around 1.

Really, the best metric is cents per mile or miles per dollar!

I have friends recently looking at the Fusion Energi. The “salesman” quoted 100MPGe is how far the battery runs on electricity. Sigh.

A bit off topic, but;

When I arrived on these fair shores in 1966, my fume-ridden beat-up Ford Galaxy cost me around 2.5 cents/mile to run.
That’s close to a Nissan Leaf’s fuel cost (for me anyway in OR) today, nearly 1/2 century later.

But the gas hog only cost me $500 (less $250 back on resale).

Let’s hear it for the gas guzzlers of yesteryear!
Oh wait. Scratch that. I’m forgetting what company I am in here.

Hmmm… 2.5 cents in 1966 is about the same as 18 cents in 2014 according to:
http://www.bls.gov/data/inflation_calculator.htm

Also, I think gas cost like 40 cents($2.89) back then too. Ah the good ‘ol days.

On any other day, I’d vote miles (or KM) per kWh. But it’s St. Paddie’s Day, so…..

I vote my favorite energy metric that powers my bike – Miles/Guinness. Both gas and electricity are just energy snakes to be driven off the emerald isle…

Here’s to you, kDwag:)

The problem with MPD is that some idiot political hack will always find some crazy penalty rate for electricity that is seasonal and only charged on really high consumption, and in only one place in the world (or whatever) and then run around quoting all EV’s as if that was what they all cost. The same way they talk about EV’s burning coal.

MPGe does suck as a metric, but at least it is predictable and bland. I don’t really think I want to hand another idiotic line of attack to those politically motivated to distort.

Very good points.

Yeah, and the political hacks on the other side might use their EPA to declare your breath “pollution”. Oh wait, never mind … they already did that.

BTW … here in IL, most of the electricity that goes into my Volt is made from clean coal. Our crops love breathing the extra C02, and I like the cheap electricity. Our air is so crystal clear, you can see for 30 miles. 馃檪

MPGe is fine. It allows you to compare the EVs against each other and it shows the dramatic efficiency improvement of EVs compared to gas cars (2 to 3 times more efficient!).

MPD would be nice but is much too hard to deal with because of variations in gasoline and electricity prices.

This may be why some people don’t like MPGe? EV’s are *already* at least 2X better than the new EPA requirements for cars in the future.

Cost per mile works fine – and that can include scheduled maintenance, too. Dealers charge set rates to do regular maintenance and it can be 3-3.5垄 per mile; added to the cost of gasoline of ~15垄 per mile.

Typical EV’s are 2-3垄 per mile, while the average car (~23MPG) is ~18垄 per mile.

Put solar panels on your house and drop the cost of driving an EV to 0-1垄 per mile – yes it can be essentially free.

Everything has been stated a dozen times by now, but my only input is with Plug In Hybrids / EREV’s – they must have two distinct measurements. One indicating the efficiency of running on Electricity, and a second for running on Gas. The combination numbers that they throw on vehicles like the PiP, Accord Hybrid, Ford Energi’s, and Volt are seriously flawed leaving consumers thinking that some of these are highly efficient when in fact they may be not that great compared to BEVs. The average rating of driving 30 miles might look great for some of these, but the difference can be better seen when comparing at longer distances – so for sure eliminate the BS metric of combined EV/gas estimates. Two measurements – electricity efficiency and approximate electric distance, then the MPG efficiency for running on gas. For that matter – I say use the Miles Per Dollar measurement for easy comparison and somewhat regionalize the approximate costs.

The other problem with miles per dollars is that would that it would vary over time. A good metric should not change over the lifetime of the car.

I care less about MPGe, or for that matter Miles Per Dollar, compared to full EV range.

If a car (BEV or PHEV) has a low EV range, it doesn’t matter how high the MPGe is. Short EV range means making use of the gas engine in a PHEV or 2nd gas car in case of a BEV. I’d rather minimize how much I need to drive on gas. I’d like to see the Environmental Protection Agency emphasize the EV range over MPGe or MPD.

I like the concept of a prior yearly average for the cost of gas/electricity. It’s intelligent and very doable. But how useful is it to compare EVs to EVs? Most EVs are right around the 3 mi/kWh (mine is 3.25). The actual cost difference between variation here is nearly negligible, and I would suggest irrelevant to marketing.

MPGe is here to stay, however, because it is what laws/requirements/taxes are based on in the US at least. It’s not designed to “sell” the car.

If the purpose is marketing, how about Cost to Fill Up?

As a sales rep, the best way to represent the emotional impact of cost is the cost of fill up from empty followed by frequency of fill up.

For a Ford Focus EV:

$2.88 to fill up from empty every other day

But most people charge daily, so it’s about a dollar a day ($1.19)

24 kWh * ~$.12. I’m aware that it’s actually 19.5 kWh of internal capacity. 12,000 m/yr or 33 m/day. Adjust for individual needs.

Numbers don’t sell cars. Emotions do.