Nissan LEAF Charging Port

Nissan LEAF Charging Port

2011 Coda Sedan prototype - charging socket

2011 Coda Sedan prototype - charging socket

Charging Port: Think City.

Charging Port: Think City.

Tesla Roadster recharging at Denver International Airport, from SolarDave blog

Tesla Roadster recharging at Denver International Airport, from SolarDave blog

At the moment, drivers of cars from the  2011 Mitsubishi i-MiEV to the 2010 Mini E are struggling to achieve the official mileage-range figures. So far, only Tesla's 2010 Roadster seems to be able to deliver on its range promises, and that's just when driven conservatively.

Why are we hearing so many tales of stranded EVs that couldn't reach their claimed mileage? Do car companies exaggerate their ranges, or are there other forces in play?

Manufacturers' range-per-charge claims are as tough to tie down as fuel economy figures. They're often obtained under laboratory test conditions, with optimal weather and road conditions, using trained test drivers.

The tests don’t take into consideration the morning school run -- under-inflated tires, a full car and heavy wind aren’t factored into the equation.

Like gasoline cars, an electric vehicle's energy use will be affected by the weather. When it rains, it takes more energy to push the car along than when it's dry. Poor maintenance, under-inflated tires, and even a stressed driver can all make a car underperform on efficiency.

Temperature also affects EV range. Many experts cite insufficient battery heating as the cause of the winter range problems of 2010 Mini E lessees last winter on the East Coast. Batteries, just like humans, like to be warm: Cold batteries are physically unable to perform as well.

Temperature range issues can be partly alleviated by better battery systems. But the way we drive can be changed by us. Learn to drive smoothly, accelerating evenly and anticipating when to slow down, and your range will increase overnight--as any EV owner will testify.

And it does matter. In a gasoline car that can do 400 miles on a tank, you may not notice a 10 or 20 mile difference between optimal and poor conditions. But those same 20 miles could mean a reduction of one-fifth the total range for an EV.

When you hear about local journalists running out of juice while borrowing an EV, it's likely their driving style hasn't adapted to EV driving. Yes, EVs should be able to be driven just like any other car--but they're not there yet.

Finally, EV batteries like to be treated right. Although they're there to be used, you need to prevent over-discharge. Maintain a healthy charge/discharge cycle and your battery will perform fine for years. Abuse it and sooner or later, you'll be plugging in before lunch.

As more EVs come to market, you can expect that they will perform close to their manufacturer's claimed range. EV makers know they need to be realistic, even conservative, about the real-world range of their vehicles.

Until we all have more experience, though, it's best to be pessimistic about claimed EV range. Until you learn first-hand how far you really can go on a charge, erring on the side of caution will save not only your car but your nerves.