This post, part of a series we're running all about electric cars, was written by Christopher Lampton from HowStuffWorks.com.
Anyone who's ever tried to start a car on a cold winter morning, cranking the ignition several times before the internal combustion engine finally chugs to life, knows that their car's battery doesn't perform as well when it's cold as it does when its warm. This is usually only a minor inconvenience in a gas-powered car because the battery plays only a minor role in the vehicle's operation. However, in an all-electric car, where the battery is responsible for running the electric motor that makes the car go, battery temperature can become crucial. If the battery is too cold the car can be sluggish or may not even move at all, and in extremely cold weather, its driving range may drop significantly. Worse, at low temperatures the battery may not even be able to accept a charge, so once it goes dead it will likely stay dead until it can be heated and charged.
But batteries don't deal well with heat, either. If the battery in your electric car overheats, it can hasten the end of its lifespan or even cause it to stop working on the spot. In extreme temperatures, the battery pack can explode, and the lithium-ion (Li-ion) batteries being used in most electric cars now in the planning stages are especially vulnerable to this problem because they pack so much energy into a small space. (This high energy density, in fact, is why electric car manufacturers like to use them.) There have even been cases of Li-ion batteries in laptop computers and cell phones overheating and bursting into flame.
For that reason, electric car makers have to devote considerable effort to keeping the vehicle's battery pack in its Goldilocks range: not too hot, not too cold, but just right. However, there is as yet no agreed-upon method for doing this. The Nissan LEAF will heat itself directly from the electric power when attached to a charger and will use an air-cooling system to prevent the battery from becoming too hot. A timer can be set to preheat the battery before the car will need to be used.
Other electric car makers believe that air cooling systems aren't sufficient and are looking toward liquid heating and cooling systems. Tesla uses one in the all-electric Tesla Roadster. The Ford Focus Electric, scheduled to debut in late 2011, will use one as well. In a liquid system, a coolant fluid is pumped through the battery to maintain the proper temperature. Once again, the charging systems for these vehicles will automatically heat the coolant fluid while the car is parked, keeping the batteries warm enough to accept a charge and well within the optimal temperature range for driving. While the car is being driven, the coolant will be chilled by the radiator to keep the batteries from becoming too hot.
The degree to which either heating or cooling will be important to an electric car depends on where and when it's being used. In the north, especially during the winter, preheating will be crucial. Further south, preheating may never be an issue, though cooling could potentially be necessary in almost any climate, because the battery can build up heat through use.