Mythbusting the world of EVs: are trip computers accurate?

MYTH: Trip computers are really inaccurate

The good news: electric cars almost always have an amazingly accurate trip computer and battery gauge. Petrol and diesel cars are congenital liars. A combustion car’s fuel gauge will stick cheerily on full for the first 100 miles. Then gravity gradually takes hold and the needle accelerates downward, finally taking a terrifying plunge from a quarter full to empty.

Whereas in an electric car, the state of charge meter is accurate. Drive in the same style, and each 10 per cent fall in the battery meter will get you the same distance. (Speed up and the next 10 per cent will get you less far, slow down or go downhill and it’ll stretch. Which is why I never look at the range-to-go meter – it doesn’t know how conditions will change.)

Combustion car average mpg readouts are hopeless. Divide miles driven by fuel pumped in, and you’ll find them 10–15 per cent optimistic. Whereas electric car miles per kWh readings are usually spot on. Zero the trip when you unplug, drive a full range, divide miles by the mpkWh readout and the resulting figure will be almost exactly the battery’s specified net capacity.

The bad news: the mpkWh figure is less than the electricity you pay for. There’s usually about a 10 per cent loss in the AC charging process. The trip computer is showing you battery-to-wheel energy consumption, not grid-to-wheel. Mind you, combustion cars suffer similar unaccounted losses. In calculating your input of petroleum, or output of CO2, you should use a well-to-wheel figure, not the tank-to-wheel number.