How does an EV calculate range?

Range anxiety has been one of the principal reasons electric vehicles (EVs) have remained a niche product in the Australian market.

But as electric cars have improved, range anxiety is not the cause celebre it once was. With newer models like the Hyundai Kona Electric reaching the market, a realistic range of 400km or more has reduced range anxiety to little more than a lingering doubt.

The Kona displays the range in kilometres in the top right quadrant of the instrument binnacle. This datapoint is akin to DTE ('Distance to Empty') in a modern internal-combustion car.

According to the importer, the Kona's range is calculated by using algorithms to massage the data from on-board sensors.

If the electric vehicle's range remaining is 100km and your destination is 50km you can rest assured the car will get you there – provided your driving style doesn't vary much, the terrain remains basically the same and you don't fire up headlights, wipers and every electrically-powered comfort and convenience feature installed in the car.

The range is always an extrapolated average. That means that the computer's range prediction is derived from translating the remaining battery charge into kilometres, based on the remaining charge as a percentage of the total battery capacity and how long the vehicle has travelled so far on that charge.

As an example, let's say that our Hyundai Kona Electric has used 30kWh of its 64kWh battery to travel 210km. Divide the distance travelled by the power used and you're left with the number seven. Multiply that by the battery charge remaining (34kWh) and you're left with 238km – which is your 'distance to empty' for the EV.

This figure can automatically rise or fall according to how much or how little energy is consumed during the preceding period or distance travelled. In other words, range is a function of driving conditions and driving style. Drive gently and the battery will last longer.

The sweet spot for the Kona's efficiency is 90km/h. When the Hyundai is switched to Eco mode, speed is limited to 90km/h and the air conditioning is switched off.

If you've been driving your EV hard for the past 50km, the computer will extrapolate that you will continue to drive the car aggressively for the next 50km (or more) and calculate the range based on that high-consumption scenario.

That being the case, the remaining range may automatically adjust downward from 150km to 100km or less. It's basically creating a 'trend line' such as you would see in a graph, with the final point of that trend line being the geographical point at which battery charge is totally expended.

Jaguar provides a very useful range calculator on its UK website to illustrate how range for the Jaguar I-PACE can vary according to the prevailing conditions. The online calculator only goes so far, however, whereas some on-board range calculators can take into account factors such as topography, for instance.

If you've been descending from a mountain summit for the past 20 minutes, the computer may decide that the car will continue to descend and it will accordingly predict a range of 250km.

But once the car is on the flat and accelerating up to speed – into a headwind – it will use more energy and the range may diminish – possibly to a point short of your destination.

In the event that 10 minutes after the car has reached the base of the mountain the driving range has dropped from 250km to 150km – and the destination is still 200km away – the driver will have to reduce speed, turn off ancillaries that draw power from the battery and hope that strategy will increase the range once more.

If the strategy works, the range will be enough to reach overnight accommodation with a recharger available – or at least a powerpoint.

Hyundai advises that driving style, the powertrain mode, the external temperature and use of the air conditioning can all have an effect on how fast the battery drains. Having more passengers and luggage on board can effect range as well. So too will headlights. Hyundai's Eco mode in the Kona Electric handles a lot of this power-conservation tasking for you.

All this sounds very complicated, but it's really no more complicated than understanding the fuel gauge and DTE in a conventional car. In the good old days, with no service stations around, early motorists were forced to check a sight glass or remove a dipstick to check the fuel, and carrying around jerrycans of fuel was just something early motorists did.

Life is made much easier with the modern motor car because service stations are on every corner and car companies cleverly design fuel gauges to read empty with a reserve amount remaining in the fuel tank.

This usually provides another 100km or so of range in an internal-combustion car after the fuel warning light has illuminated. Long gone are the days when your late-sixties Ford Cortina would die within 30 seconds of the fuel gauge needle nudging 'E'.

The car companies are getting smarter with range prediction for their EVs as well. To improve range prediction accuracy in its electric vehicles, Tesla has recently introduced a new algorithm that includes elevation and ambient temperature along with other factors in deciding the vehicle's remaining range.

Mercedes-Benz has revealed that its EQC can estimate the range with a high degree of accuracy if the driver uses the satellite navigation to find the destination. Using the route data, the EQC can calculate the range accurately from not only distance and driving style, but also the lie of the land along the route – before the EQC gets there.

At present, Tesla models will choose a route serviced by Tesla Superchargers if the distance to the destination is too far on one battery charge. But before long, as the rollout of EV chargers progresses and battery technology improves, range calculation for electric cars could become a relic of the past, like the sight glass and the dipstick.

Bit of an expert with a spreadsheet, are you? Try this, it's easy.

Type an EV's battery capacity in kilowatt-hours into cell A1 of a spreadsheet.

In the cell immediately below it, cell A2, type in a figure for energy used in kilowatt-hours per 100km.

Finally, in cell A3, paste this formula: =(A1/A2)*100

Using the Kona Electric as an example, the battery capacity – in cell A1 – is 64. The official power consumption from Green Vehicle Guide for the Kona – for cell A2 – is 13kWh. If you spend more time on the open road than around town, type a figure of 16 into cell A2, or if you drive aggressively and use the headlights, wipers and climate control to the max, settle on 18 instead.

If you own a Mitsubishi i-MiEV, type 16 into cell A1. For a BMW i3 use 27, for a Kona Electric use 64 and for Tesla Model S use 60, 75, 85, et cetera – whichever applies.

The result in cell A3 should tell you roughly how far you can expect to travel from one battery charge to the next. You can play around with numbers in the top two cells to see how the range might vary.