An electric car as a second car: when the sums work

Nearly every objection to electric cars concerns the exception: the long holiday drive, the trailer, the cross-country trip at minus fifteen. In a two-car household those exceptions fall to the other car. What is left is everyday use — short, repeated, predictable journeys.

That profile is exactly what an electric drivetrain is built for. Short trips are the worst case for a combustion engine: it runs cold, uses disproportionately more fuel, and neither oil nor exhaust aftertreatment reaches working temperature. An electric motor has no such state; it is at its best point from the first metre.

The second point is range, and here it disappears. Drive thirty kilometres a day and charge overnight and you start every morning full. In daily use an electric car's range is not the distance to the next charger but the distance between two nights.

The whole calculation rests on one condition: the car must be able to reach electricity where it stands overnight. Without it, the economical second car becomes one that has to be driven to a public charger regularly — and the time alone kills the idea before cost even comes into it.

For a second car, less is often enough than people assume. At thirty to forty kilometres a day a domestic socket with an emergency cable is arithmetically sufficient: two kilowatts over eight hours is sixteen kilowatt-hours, more than such a trip uses. A fixed installation is still the sensible answer, because a domestic socket is not built for daily sustained load.

If you rent or live in a shared building, settle this before buying rather than after. It is usually solvable, but it takes time — and that time belongs in the plan.

In a household's main car a large battery is an advantage; in a second car it is usually unnecessary weight and unnecessary money. A battery used to half its capacity each day and topped up each night does not need to be large — it only needs to cover the daily demand with a margin.

A small battery is lighter, which is easier on tyres and suspension, it is cheaper to replace if things go wrong, and it fills in reasonable time from a weak supply. And it has an advantage that is rarely mentioned: for the same daily distance it sees more cycles, but each of them is shallower if you keep it in a middling charge window overnight.

The charging time calculation is simple and needs no electricity price: daily distance times consumption per kilometre gives the energy to replace; divided by charging power that gives the hours. If the result fits into one night, the charging question is answered.

Two points argue against it, and both concern winter. First, winter loss hits a small pack the same in percentage terms but harder in absolute ones: a third of two hundred kilometres leaves more margin than a third of a hundred and twenty. With a small battery, do not also plan tightly in winter.

Second, fast charging power scales with capacity. Because the cell only tolerates a given C-rate, a small pack charges at fewer absolute kilowatts than a large one. For daily use that is irrelevant, because you charge at home. For the occasional longer trip it is the reason that trip goes to the other car.

The third point is not a drawback of the small battery but a characteristic of older cars in this class: many have no active liquid cooling. They are more sensitive to heat and to repeated fast charging. As a second car charged overnight that hardly matters — as a car fast-charged daily it would.

A second car stands still. That is its nature, and it has consequences that appear in no consumption calculation. Lithium-ion cells age without use, and that calendar ageing depends on two things: temperature and state of charge. Warm and full is the worst combination, cool and part-charged the best.

In practice: a car left for weeks at ninety per cent in the sun ages faster than one at sixty per cent in a cool garage. If you regularly leave the car for longer periods, set the charge limit accordingly and top up before the next longer trip — most cars allow this.

The second point about standing is the twelve-volt battery. It supplies the control units and is only topped up from the traction pack when the car wakes up regularly. Cars left unmoved for months typically do not have a high-voltage problem but a flat twelve-volt battery — and without it the car will not switch on.

A second car brings a second insurance policy, a second vehicle tax, a second roadworthiness test, a second parking space and a second set of tyres. Those fall due however little you drive — and they are why a second car rarely pays at very low annual mileage.

Vehicle tax is assessed, depending on the country, on weight, power, engine size or CO₂ emissions; battery-electric cars are subject to separate rules in many places, sometimes for a limited period. Which rate and which period apply where you live is a question for the vehicle licensing or road traffic authority — which is also where the current position can be looked up.

On insurance, comparing pays more than it does for a first car, because many insurers rate a second vehicle of the same owner differently and because the rating of an electric car varies widely between them. That is half an hour's work with an effect every year.

The saving arises in the variable costs, at three points. The first is energy: a kilowatt-hour from your own socket costs a fraction of what the same distance costs at the pump — how much exactly depends on your own tariff, which you have to put in yourself.

The second is servicing. There is no oil change, no cambelt, no spark plugs, no exhaust and no particulate filter. The inspection checks brake fluid, the coolant circuit, software, the cabin filter and the high-voltage connections. The scope is smaller, and at low annual mileage it is driven by time rather than distance.

The third is brake wear, and on a town-bound second car it stands out: much of the deceleration goes through regeneration, so pads last a long time. The flip side is that discs are more likely to rust than to wear — which is why an occasional firm brake application belongs in the routine, and why disc condition is the point that matters at the inspection.

This is exactly where the used market is interesting, because early small cars with small batteries were expensive new and trade cheaply today. The price mostly reflects one thing: uncertainty about the battery. Remove that uncertainty and you buy better.

Four points settle it, and all four can be done before the test drive:

There are situations where the answer comes out negative, and they are easy to spot. Without somewhere to charge at the parking space it does not work. At very low annual mileage it does not work, because fixed costs dominate. And it does not work if the supposed second car in fact has to take the long trips regularly, because the other car is not available.

Conversely: anyone driving twenty to sixty kilometres a day, with a socket at the parking space and a second car in the household for the exceptions, has the case where the sums work out most clearly — and without needing to know a single electricity price.