Evaluating Electric Vehicle Range Claims

We all know that the mpg claims on a new car’s sticker are optimistic rather than realistic, although we also all know that if one is to drive particularly gently and at slower than normal speeds, one can be reasonably sure of achieving the stated mpg numbers.

Furthermore, the worst case scenario of finding that your new vehicle with say a 15 gallon tank and a claimed fuel economy of perhaps 35 mpg, but only does 33 mpg, isn’t very life changing.  Over a typical 12,000 miles of driving a year, you wouldn’t need even two more tanks full of gas, and spend (at say $2.80/gallon) an extra $58.

Things get more serious for an electric car; not so much cost-wise as convenience-wise.  For a regular internal combustion engine (ICE) powered vehicle, there is a choice of about 115,000 gas stations in the US, with a tank fill taking 2 – 3 minutes (at typical flow rates of 6 – 8 gallons/minute).  In other words, each minute of pumping can get you 150+ miles of extra driving.

For an electric car, there are many fewer charging locations, and of those charging locations, most are slow – instead of 150 extra miles of gas per minute, you get more like 0.6 miles per minute (ie a 50A 220V circuit) of charge.  Some are even slower – if charging on a regular home circuit (110V 15A) you can expect 5 miles of charge per hour.

The other thing is if you turn up at a regular gas station and all pumps are in use, you only have to wait a few minutes for a pump to come free.  If you turn up at an electric recharge site, you might find yourself waiting 30 – 60 minutes for your turn, occasionally even longer.

The difference for an electric car with either 250 and 230 miles of range per charge can be profound.  Due to the sparse nature of charging stations, you can’t plan on running the vehicle until within 20 – 30 miles of empty then looking for a charging station.  You might need to recharge 100 or more miles before empty, so that means the difference between 130 and 150 miles between stops.  That doesn’t matter when you’re driving around town and can charge at home, overnight, every night, but if on an extended roadtrip, that’s a huge difference in the number of stops and the time spent charging.

Sure, there are moves afoot by the Biden administration to boost the number of fast charging stations across the country, and the marketplace will in any event (more slowly) react to the growing number of EVs and need for charging.  But until new battery technologies come along that allow for longer range (slowly improving), faster charging (moderately difficult), and until new power delivery technologies come along that can dump 60 – 100 kWhrs of power into your battery in five minutes (extremely difficult), recharging an electric vehicle as part of a roadtrip is always going to be an inconvenience best minimized.

The other thing is that with a regular ICE powered vehicle, if you run out of fuel, that is only a minor hassle.  Many people do – AAA report that about half their 32 million calls for roadside assistance each year are for drivers who ran out of gas.  As soon as you can beg/borrow/steal a gallon or two of gas, you’re back on the road again and able to get to a gas station.

With an EV, if you run out of charge, things are more complicated.  Some AAA trucks now have a fast charge capability that will give you ten miles of range in about ten minutes.  That’s great, but what if there is no charging station within ten miles?  Do you have to place another call for another ten miles of range?  Will the AAA truck have recharged its onboard charger yet?  The only other option is to be towed to the nearest charging station, and with tow rates in the order of $5 – $10/mile, that gets very expensive very quickly.

Most people, when planning a roadtrip with an EV, like to be able to map out a route in advance (this is a great service) and designate charging stops as part of their schedule.  For this reason, it is important to accurately know the range of your EV.

Of course, after owning an EV for a while, you’ll get to know the “real” range of your EV when driven the way you like to drive.  But if you’re at the start of the EV owning process, you probably want to understand just how trustworthy the claimed range figures published alongside EVs actually are.

How an Official EV Range is Calculated

The EPA is the US government agency responsible for testing all types of vehicles and reporting on their fuel economy (the other side of the “range” coin).  In the case of electric vehicles, it quotes fuel economy in terms of MPGe – an equivalent rating showing what it would get per gallon of theoretical petrol if it was using petrol rather than electricity.  The concept of MPGe is rather irrelevant and meaningless, but the same as MPG, the higher the number, the better.

(As an aside, did you know most countries in the world these days don’t use miles per gallon, nor even kilometers per liter, instead they use liters per 100 kilometers, which means lower numbers are better than higher numbers.)

Just like with regular cars, an EV sticker shows two figures – one for highway driving and one for city driving, plus a combination of both with 55% of the “average” being city driving and 45% being highway driving.  Here is a list of their present ratings.

The calculation is not done “in real life”.  It is based on running a fully charged EV on a dynamometer on a specified sequence of speeds and times, using up the entire charge, then recharging the vehicle to see how much power was consumed to “drive” (on the dynamometer) the distance covered.

Not doing it in real life is actually a good thing.  Doing it in a testing laboratory makes for consistent results not influenced by weather, road surfaces, other traffic, and so on.  But the consistent results are only valid if they fairly mirror how you are likely to be driving your EV.

There are two different sequences, one for city driving and one for open road/highway driving, with different types of driving in each.

The EPA then recognized that spinning a dyno is much easier than driving in the real world, with more friction, wind resistance, and other factors, so multiplies the calculated number by 0.71 to reduce it down to something more resembling the real world.

Note that other countries use different testing methods so be sure, if comparing numbers, they are all being expressed in terms of the same testing protocol.

There are two other frequently encountered measures – the New European Driving Cycle (NEDC) and the very grand sounding Worldwide harmonized Light vehicles Test Procedure (WLTP).  This article discusses the differences.  Perhaps surprisingly, other testing methods provide higher theoretical range figures than the EPA range numbers.

Now for an interesting twist.  Much of the time, the EPA does not do this testing, itself.  Instead, the car manufacturer does, and advises the EPA of its findings, which the EPA accepts on trust.  That trust is not always justified, as we mention in the next section.

What a Range/Fuel Economy Rating Does Not Guarantee

The testing is designed to create a standard test with a standard result that approximates, more or less, the type of performance that actual drivers might experience.

But it does not guarantee that any vehicle will achieve exactly the results claimed, other than if the test were to be repeated in another laboratory and on the exact same testing basis.  That is the only guaranteed element.

So you can’t normally sue either the EPA or car manufacturer for publishing a range figure that you don’t get in actual driving.  Well, you can’t, unless you can show that the published figure is also not achievable in the formal EPA testing – ie, that the car manufacturer may have been, ahem, “overly optimistic” in how they “interpreted” the results of their own testing….  There have been successful suits brought against conventional car manufacturers who became “overly optimistic” in their calculations and claims – for example this (and many other) claims.

It seems Tesla in particular is markedly optimistic in its range claims.

The EPA numbers quoted are definitely “best case” scenarios.  You’ll immediately observe, for example, that for the highway test, it assumes an average speed of 48.3 mph (coincidentally, no doubt, also the speed at which ICE powered vehicles are thought to be at their most efficient and economical) and a maximum speed of 60 mph (air resistance increases with the square of speed – you get a much better result by having an average of 48.3 and a max of 60 than you do by keeping the average but having a max of 70 or 80).  In Washington, on longer drives, our freeways are rated at 70 mph and over the course of many hours at a time, most of us are averaging, well, let’s just say, more than 70 mph.  I know someone who averaged 80 on a 250 mile freeway drive this week…..  So the highway fuel consumption calculation has little reality to what a real person gets, driving at real speeds, in the real world.

The Startling Difference in EV Fuel Economy Ratings

We have come to understand that ICE powered cars always get less fuel economy when driving around town.  Every time we apply the brakes, we’re in effect throwing away the benefit of the fuel we burned to get to that speed, and every minute we’re stopped, idling, we’re using fuel while going nowhere.  Even when we’re driving at steady speed, at 25 – 40 mph, those are inefficient speeds that usually don’t give as good an economy as faster speeds may.

On the open road, we get up to efficient operating speeds and then enjoy steady driving with much less braking and (hopefully) little or no time spent stopped in traffic.  Hence the better fuel economy for highway driving.

But an EV has regenerative braking.  When you use the brakes, the motor swaps from using battery power to speed up the vehicle, and instead uses the speed, to generate power, and slows the vehicle down in the process.  Depending on how hard you’re braking and certain other factors, you can get back as much as 70% of the energy you originally used to speed the car up when you use regenerative braking to slow down again.

The other huge difference is that EV motors are as efficient at low speeds as they are at high speeds.

These factors transform the energy use for around town driving.  The slow speeds are just fine for an electric motor, there’s no energy used while sitting at a traffic light, and the energy used to speed up is largely reclaimed when you slow down a short time later.

So city driving becomes more economical than long distance freeway driving for an EV.  For example, the Chevy Bolt gets 124 mpge around town but only 102 mpge on the highway, and its range is based on a combo rating of 113 mpge.

The Tesla Model 3 gets 150 mpge around town and 133 mpge on the highway, with a combined rating of 142 mpge.  The new VW ID.4 gets 104 mpge around town and 89 mpge on the highway, and a combo rating of 97.

So you can see that right away, the official range stated for an EV is going to be less when you’re driving on a freeway, whereas with a regular car, we’re used to expect our economy/range on the freeway.

That is very disappointing, and also potentially impactful.  If all you’re doing is driving 50 miles a day to and from work, it really doesn’t matter what amount of your charge is being used if your EV is rated for about 250 miles of driving.  But when you’re driving 400 miles, it makes a big difference in terms of where you’ll need to plan to refuel, and how long you’ll need to spend refueling at each such stop.

And that’s just the start of the bad news.

Factors that Modify (Reduce) Your Electric Vehicle’s Range

So we’ve already discovered that freeway driving cuts down on your theoretical range.  The difference in EPA calculated theoretical economy and range between the blended range and the freeway driving might be around 5%, maybe even 10%.

But remember that freeway driving assumes you’re averaging 48.3 mph – the often thought to be “sweet spot” for optimum fuel economy in an ICE powered car.

EVs don’t have a sweet spot – pretty much from 1 mph and up, the faster you go, the worse their fuel economy (I’m simplifying, there are some fixed loads and other factors too), but they do share the inevitable growing impact of wind resistance as speed increases.  If your speed doubles, wind resistance increases four fold – ie, it increases as the square of the speed.

So going from 48.3 mph to 75 mph as an average speed sees wind resistance increase 2.4 times.  Unsurprisingly, this means that fuel economy and therefore range massively decreases.  It doesn’t decrease 2.4 times, because there are other factors that remain more steady and unrelated to speed, but it does greatly decrease.  Tesla used to publish an excellent online calculator that would show the expected range for its vehicles based on whatever average speed you chose, but that was discontinued many years ago.  Here’s an article that has some screen shots from it – it was a wonderful tool and we can only think dark thoughts about why it was discontinued.

There is an independent site that has published some range data for various different Tesla models.  The data may or may not be exactly accurate, but it gives you a good sense for the impact of speed on range.  This seems like a good “do it yourself” estimator.

Testing by Car and Driver Magazine, running vehicles at a constant 75 mph, showed actual ranges achieved could be as much as 40% less than the claimed EPA combined range claims.  A much kinder test by Inside EVs, and at 70 mph, showed much smaller differences, and the Porsche vehicles actually provided more miles than claimed.  Maybe part of the reason for the much better results in the Inside EV testing is due to the slower speed used.  It seems that each 5 mph difference in speed represents just under a 10% difference in range.

Another important variable can be temperature.  Your batteries work best when they are between about 59°- 95° F (15° – 35°C), and ideally, closer to the low end of that scale.

Going outside that temperature range means your batteries will deliver less power per charge, and may age (in other words, their capacity to store power will reduce) more quickly. If in a cold environment, the good news is using the car will cause the batteries to slowly heat up; but that good news becomes bad news in a hot environment, where battery temperatures can shoot up above the outside air temperatures.  Some electric vehicles include either or both battery heating and cooling, although this in turn requires battery power to run.

Depending on your driving style and situation, very cold weather can see your range drop by 10% – 30%.

We mentioned batteries aging, and storing less and less power each time they are charged and discharged.  There are three things to avoid if you want to get maximum battery life.  Unfortunately, these three things are all incompatible with roadtrip type driving :

1.  Don’t charge batteries to full capacity.  Stop at 90%, better still, stop at less than that.

2.  Don’t discharge batteries all the way to empty.  Recharge them while there is at least 10% of charge still in them.

3.  Don’t charge them too quickly.  A full charge should always take more than an hour with current battery technologies.

Tesla in particular have rapid chargers that are very convenient, but are also hard on the batteries.

So if you’re only charging to 90% and discharging to 10%, that means you’ve given away another 20% of your range.  And if you’re slow rather than fast charging, it becomes less convenient and takes more time to recharge your batteries as needed.

Generally it seems that with attention to these details, it is realistic to expect in the order of 500 full battery recharges (or 1000 half charges) before the batteries start to show a significant decline in storage capacity.

How much is “significant”?  Tesla’s battery warranty promises that its batteries won’t drop in capacity by more than 30% during the eight year and variable mile warranty period.  Oh – the fine print says that if you have a battery warranty claim, Tesla won’t necessarily give you a brand new battery – it merely promises to replace your battery with another one that still has at least 70% of remaining capacity.  GM has an 8 year/100,000 mile warranty on its Bolt battery, but allows the battery to lose 40% of its charge during that period.

Many people who are careful with the battery are reporting much better life and massively less loss of capacity than the warranty coverages guarantee, but even so, as your vehicle ages, its range will be slowly but steadily dropping.

This chart here collates a number of reports from Tesla owners and gives a good general sense about what is happening to Model S/X batteries.

As an aside, there’s an interesting benefit from a car with a longer range.  Remember that battery life is limited not by miles driven but by the number of battery charges done.  So if you have two cars, one with a 200 mile battery and the other with the 400 mile battery, and if they both have a similar battery life in terms of recharges, the 400 mile battery, because it is only being recharged half as often, will last twice as long.

Maybe you’re wondering how much a new battery pack will cost.  A quick internet search shows claims that a Tesla Model 3 battery pack will cost between about $3,000 and $7,000.  But note the careful phrasing “it is estimated” and the very unprecise range of costing estimated.  Keep looking, and you’ll uncover that the real exact replacement cost – and not for a new battery, but for a remanufactured one, including the labor to replace it as well, was actually $16,550.67.

So if you replace your battery once every 200,000 miles, that represents a cost of 8.3c a mile for the future battery replacement cost.  That’s not something you’ll see factored in to most of the “fan” articles showing how much less expensive a battery powered car is than an ICE car.

Other drains on the battery, and therefore reduction in range, include in-car heating, and to a lesser extent, in-car cooling too.  Not so important are having the headlights or sound system operational – if you’re on the freeway and charging up the car every 3 – 4 hours, there’s not a huge percentage of the battery power being used by lights, music, and other electronic devices.

All the usual things of course also impact on mileage – the type of tires, their inflation pressure, the type of road surface, hills, snow, prevailing winds, and so on.

So What Is Realistic?

Around town, in moderate to warm weather, you should expect to get close to and possibly more range than the EPA blended range estimate, and reasonably close to their city driving number.

Cold winter driving at high speed on the freeway in a two or three year old vehicle could see you getting less than half the EPA rated mileage.

Can You Rely On the Range Estimate Displayed on the Vehicle’s Dash

In the older days, it seemed all ICE cars had the same type of fuel gauge.  It would read full even when the tank was down to only 3/4 full, and, more alarmingly, when it showed 1/4 full it probably had only 1/8th of a tank left.  The gauge was always an estimate rather than a genuine statement of fuel remaining.

These days, many modern ICE cars have a fuel gauge that isn’t actually showing you how much fuel remains – the display varies to give you more a sense of how many miles of driving are remaining, but shown as a fraction of a full tank of petrol.

For EVs, there is a range display that shows how many miles the vehicle is expected to be able to travel before it runs out of power.  It is probably making an assumption that your driving will be either normal or the same as you have been recently driving, although it seems the range estimators in EVs vary widely in terms of their intelligence.

If the gauge is showing 100 miles of range remaining, and you now have a 20 mile steep uphill climb, it will maybe only show 60 miles of range remaining.  But then you go 20 miles down the other side of the hill, and you see you’ve still got 60 miles of range at the bottom.

These types of external factors are things you need to consider, yourself, to adjust from the theoretical to the actuality of the driving style and terrain/weather/etc.

As the range goes down, the gauge sort of becomes more accurate.  Whereas a 20% inaccuracy, at 250 miles, means a 50 mile potential variation in range, at 25 miles, it only means a five mile variation.

Unlike old ICE fuel gauges that were never very accurate, anywhere on the scale, the range estimate of the vehicle can be very accurate, but is never any more accurate than the assumptions it is making.

You’ll learn the idiosyncrasies of how your vehicle’s range calculation works and as you understand them, you can get “adjusted by you” range estimates that are very accurate.

What to Do if You’re Running Low on Charge

Some of us sometimes carry a spare can of gas in the trunk.  A five gallon tank can get most vehicles another 100+ miles of range, and takes up little space.

Sadly, that’s not possible with an EV.  To illustrate, think of a typical external battery pack used to recharge phones and other portable devices via a USB connection.  One of those, about half the size of a paperback book, might have 20,000 mAhr of charge, which at 3.7V translates to about 75 watt hours of charge.  A typical EV goes just over 3 miles per kWhr, so you’d need at least 40 of those charger packs to go ten more miles, and that’s without thinking about how long it would take to transfer their energy into your vehicle or how long it would take or how much power would be lost as a result of inefficiencies in the charging process, or the probable $750+ it would cost to buy them from Amazon, or the hassle involved in keeping them always fully charged for that “once in a blue moon” time when you needed to use them.

The most important thing to do if you’re running low on charge is usually to slow down.  Whereas ICE powered vehicles are most economical around the 50 mph point, EVs continue to get more economical, the slower you go.

The exception to that is if you’re running A/C or heating, headlights, and/or other power drains.  The slower you go, the bigger a percentage of total power they become.  Of course, turn them off if you can, but don’t go driving with no lights on in the dark, and don’t freeze to death in the winter.

One desperate thought to seize upon.  We know that Tesla builds in a few extra “emergency” miles into its range calculations – you can usually drive another 5-10 miles once it shows 0 miles remaining.  We don’t know about other EVs, but we believe some might also have a very few miles still available after you reach zero.  Hopefully you’ll never have to find out, because it is not good to discharge the batteries fully.

One idea is that if you know you’re going to run out and there’s nowhere you can go to get some more charge between where you are when you finally realize and accept you’ve a problem, and where you’ll run out of power, you could consider “phoning ahead” to arrange for a tow truck to meet you somewhere, hopefully with an emergency power charger, or otherwise, to tow you to a charger.

I’ve always had to wait at least 30 minutes, and sometimes two hours or more, for a tow truck to come for any reason.  So when you’re thirty minutes away from empty, why not decide where a good meeting point is (freeway exit, rest area, or whatever) and call ahead to book a tow/charge service, thereby saving yourself 30 minutes of waiting.

Summary

The true range of a battery/electric powered vehicle is much more critical to accurately understand than is the case with a regular petrol or diesel powered vehicle.  It is also more dependent on weather and driving style than a regular vehicle, and surprisingly, gives better economy around town than on the open road.

If you’re driving “with the traffic” on freeways, you’ll probably find the EPA official highway range claim is too optimistic.

The actual drivable range before needing to recharge is of course shorter than the “distance to empty” number, because with electric charging stations still being few and far between, you need to keep many more miles of charge in reserve than you need to with gas powered vehicles and omnipresent gas stations.