How Electric Car Batteries Work

Image Gallery: Beijing

City street scene in Beijing, China.
Phil Walter/Getty Images
Smog, haze and heavy traffic fill the city roads in Beijing, China. See more pictures of Beijing.

A car can be a wonderful thing. It can take you where you want, when you want -- even when those places aren't served by public transportation. In fact, much of modern life would be impossible without cars. They help us get to our jobs, schools, grocery stores or even just to the local shopping mall. Unfortunately, as wonderful as cars are, they also have some serious drawbacks. Two of these drawbacks are that they often cost a lot of money to maintain and they pollute the atmosphere with noxious gases. Air pollution has become a serious problem in many urban areas, and with gasoline prices at record highs, the internal combustion engine may soon be a luxury that society simply can't afford.

Few people would advocate giving up cars altogether, but is there a way we can have the power and convenience of an automobile without the pollution and expense caused by burning gasoline? Fortunately, there is. Many people think that the cars of the not-so-distant future will be powered not by gasoline, but by electricity. In fact, these electric cars -- also known as EVs or electric vehicles -- aren't futuristic at all. Electric vehicles have been around since the first half of the 19th century; however, even now in the 21st century, internal combustion engines still rule. But why haven't electric cars caught on?

Learn More

The heart of an electric car is its battery. Unlike the batteries in
most cars, which primarily serve to start the engine and run accessories like the radio or air conditioner, the battery in an electric car runs everything. Most importantly, it runs the electric motor -- or, more precisely, it runs a controller which in turn runs the electric motor -- so it needs to be powerful and long-lasting enough to take drivers where they need to go with a minimum of recharging. Until recently, no reliable, mass-producible batteries have been manufactured that could make electric cars competitive with gas-powered cars. However, that's beginning to change. Electric cars have not only become feasible, but they're now expected to start rolling off the assembly lines of major automobile manufacturers.

Read the next page to find out if batteries will ever be a practical way of powering an automobile.


Types of Electric Car Batteries

A battery is a device for storing chemical energy and converting that chemical energy into electricity. A battery is made up of one or more electrochemical cells, each of which consists of two half-cells or electrodes. One half-cell, called the negative electrode, has an overabundance of the tiny, negatively charged subatomic particles called electrons. The other, called the positive electrode, has a deficit of electrons. When the two halves are connected by a wire or an electrical cable, electrons will flow from the negative electrode to the positive electrode. We call this flow of electrons electricity. The energy of these moving electrons can be harnessed to do work -- running a motor, for instance. As electrons pass to the positive side, the flow gradually slows down and the voltage of the electricity produced by the battery drops. Eventually, when there are as many electrons on the positive side as on the negative side, the battery is considered 'dead' and is no longer capable of producing an electric flow.

The electrons are generated by chemical reactions, and there are many different chemical reactions that are used in commercially available batteries. For example, the familiar alkaline batteries commonly used in flashlights and television remote controls generate electricity through a chemical reaction involving zinc and manganese oxide. Most alkaline batteries are considered to be a disposable battery. Once they go dead, they're useless and should be recycled. Automobile batteries, on the other hand, need to be rechargeable, so they don't require constant replacement. In a rechargeable battery, electrical energy is used to reverse the negative and positive halves of the electrochemical cells, restarting the electron flow.

Automobile manufacturers have identified three types of rechargeable battery as suitable for electric car use. Those types are lead-acid batteries, nickel metal hydride (NiMH) batteries, and
lithium-ion (Li-ion) batteries.

Lead-acid batteries were invented in 1859 and are the oldest form of rechargeable battery still in use. They've been used in all types of cars -- including electric cars -- since the 19th century. Lead-acid batteries are a kind of wet cell battery and usually contain a mild solution of sulfuric acid in an open container. The name comes from the combination of lead electrodes and acid used to generate electricity in these batteries. The major advantage of lead-acid batteries is that, after having been used for so many years, they are well understood and cheap to produce. However, they do produce dangerous gases while being used and if the battery is overcharged there's a risk of explosion.

Nickel metal hydride batteries came into commercial use in the late 1980s. They have a high energy density -- that is, a great deal of energy can be packed into a relatively small battery -- and don't contain any toxic metals, so they're easy to recycle.

Lithium-ion batteries, which came into commercial use in the early 1990s, have a very high energy density and are less likely than most batteries to lose their charge when not being used -- a property called self discharge. Because of their light weight and low maintenance requirements, lithium-ion batteries are widely used in electronic devices such as laptop computers. Some experts believe that lithium-ion batteries are about as close as science has yet come to developing a perfect rechargeable battery, and this type of battery is the best candidate for powering the electric cars of the near future. A variation on lithium-ion batteries, called lithium-ion polymer batteries, may also prove valuable to the future of EVs. These batteries may eventually cost less to build than lithium-ion batteries; however, at the present time, lithium-ion polymer batteries are prohibitively expensive.

Perhaps the greatest problem associated with electric car batteries is recharging them. How do you charge an electric car battery? More importantly, where do you charge an electric car battery? Can you do it yourself? Can you do it at home? Read the next page to find out.


Electric Car Charging

A rechargeable battery is useless unless you have a place to recharge it. If you're running out of juice in your electric car, you can't just make a quick stop at the local gas station -- unless your local gas station has a place where you can plug it in. Unfortunately, recharging the large array of batteries in an electric car can take several hours, and most gas stations would prefer that you didn't block their lanes for
that long.

The best solution to the recharging problem is to take the car home in the evening and plug it in, similar to the way you might plug in a laptop computer or digital music player, so that it can recharge overnight. EVs will come with charging systems that allow them to recharge from a standard electric socket so that the next morning you'll be ready to hit the road again. Although at least one company claims to be developing systems that can recharge an electric car in 10 minutes, existing rechargers take between
3 and 10 hours to bring an electric car battery up to full strength using normal home electricity
[source: Fehrenbacher].

An electric vehicle charging station
Daniel Berehulak/Getty Images
A man charges his electric vehicle at a charging station in London, England, on August 13, 2008.

Once an EV has been recharged, how far will it go before it needs to be recharged again? This depends on a number of factors, including the type of battery in the vehicle. EVs using lead-acid batteries have the shortest range -- around 80 miles (128.7 km) on a single charge. NiMH batteries turn in a better performance, with a range of about 120 miles (193.1 km) per charge. This is where lithium-ion batteries excel, with a range of more than 220 miles (354.1 km) per charge -- using the Tesla Roadster as an example. If driving distance is the most important consideration, lithium-ion batteries are the ones
to choose.

The range of an EV can be extended even further with a technology known as regenerative braking, which uses the kinetic energy of the car's brakes to recharge the battery on the fly. Under optimum driving conditions, regenerative braking can extend the car's range up to 50 percent, though in most situations the gain in driving range will be smaller.

But what if you want to take a longer trip in an electric car and won't be home for an overnight recharging session? Will there be somewhere you can plug it in? Very few recharging stations exist at present, but manufacturers of electric cars are planning to build charging stations so that the infrastructure will be in place when customers start driving electric vehicles. Tesla Motors, the maker of the all-electric Tesla Roadster, has made a deal with a major hotel chain to have recharging stations available for patrons who want to recharge their Roadsters overnight. One advantage of recharging stations is that they may be able to recharge cars more quickly than a home recharging system can, though it's unlikely that vehicles will be in and out as quickly as at a gas station. Unfortunately, it may be a while before enough recharging stations are available to keep EV owners recharged on long road trips. In the near future, EVs will be best suited for commuting to work or school and for local travel and shopping trips. When used in this manner, the car will be tucked safely in the garage each evening for an electrical fill-up.

Up next, find out some of the advantages -- and yes, even some of the disadvantages -- of going


Advantages and Disadvantages of EVs

The most obvious advantage of electric car batteries is that they don't produce the pollution associated with internal combustion engines. However, they still have environmental costs. The electricity used to recharge EV batteries has to come from somewhere, and right now, most electricity is generated by burning fossil fuels. Of course, this produces pollution. But how does the pollution produced by burning fossil fuels to recharge electric car batteries compare to the pollution produced by internal combustion engines? According to the Electric Vehicle Association of Canada, or EVAC, even EVs recharged from coal-powered electric generators cut carbon emission roughly in half. EVs recharged from cleaner forms of electrical power generation, such as hydropower and nuclear plants, can reduce carbon emissions to less than one percent of those currently produced by internal combustion engines. So, even in the worst case scenario, cars operated by EV batteries are cleaner than gas-powered cars.

Charging cable for an electric car
Karen Keczmerski/iStockphoto
It seems like batteries are a practical way of powering a vehicle. What are the advantages and disadvantages?

Another important advantage of battery-powered motors over gas-powered engines is the lower cost of the fuel -- that is, electricity for EVs and gas for the internal combustion engines. The United States Department of Energy has calculated that a typical EV can run for 43 miles on a dollar's worth of electricity. Only a substantial drop in the cost of gasoline could give gas-powered cars anywhere near such a low cost per mile.

Yet another advantage of these rechargeable batteries is that they recycle well. Almost 100 percent of these batteries can be recycled, which keeps old batteries from becoming a disposal problem.

The major disadvantage of battery-powered cars, as we mentioned in the last section, is the time required to recharge the batteries. With lithium-ion battery technology, a fully charged EV can travel a distance comparable to an internal combustion engine vehicle with a full tank of gas, but it still needs to be placed on a recharger at the end of that time. At present, this means a drained EV will be out of service for several hours before it's fully recharged. Of course, this is a serious disadvantage. In the future, faster recharging technology may become available, but in the near term, electric cars won't be the vehicles of choice for long trips. Even so, most driving is done relatively close to home and for this reason, battery power will serve as well as gasoline power. A possible solution to the recharging situation may be battery-replacement stations, where instead of recharging your EV you can simply swap your drained battery for a fully charged one. This system would allow batteries to be recharged outside of vehicles and would greatly reduce the amount of time required to get an EV up and running again after its battery is fully discharged.

Another disadvantage of electric car batteries is their weight. Because they need to do more than traditional car batteries, electric car batteries need to be linked together into arrays, or battery packs, to provide additional power. These collections of batteries are heavy. The lithium-ion battery pack in a Tesla Roadster weighs about 1,000 pounds (453.6 kg). That's a lot of weight to carry and it can greatly reduce the car's range. However, the designers of the Roadster have offset this battery weight with a light frame and body panels. The entire car only weighs 2,690 pounds (1220.2 kg) -- not terribly heavy when you consider that more than a third of that weight is battery.

Given the importance of the battery to an electric car, you might wonder what will happen as that battery grows older. How long will it be able to power the car? And when it finally dies, can it be replaced or is it simply more economical to buy a new car? Read on to find out.



The Lifecycle of an Electric Car Battery

How long will an electric car battery last? The lithium-ion battery pack in the Tesla Roadster is projected to have a lifespan of about 5 years or 100,000 miles. At the end of that time the pack will need to be replaced, at a cost of approximately $10,000. Sure, that's expensive, but the Roadster itself will cost almost $100,000, which makes the cost of the battery pack seem affordable. Many, perhaps most, owners will no doubt prefer to replace the battery pack rather than buy a brand new Roadster.

Tesla Motors
Justin Sullivan/Getty Images
The 2009 Tesla Roadster is an all-electric, zero emissions vehicle capable of traveling nearly 250 miles on
a single charge.

Admittedly, battery maintenance costs will add to the expense of operating any EV. The battery packs that are used in EVs will be kept tightly contained, so you'll most likely need to take your EV to the dealership to have your battery serviced. Another point to consider is that at the present time, this is a relatively new technology. As EVs become more common on the roadways, some of the high prices associated with them will decrease. But right now, the Tesla Roadster's $10,000 battery is one of our only reference points. Will the batteries in other EVs cost more? Will they cost less? Will the cost of replacing the battery in some EVs outweigh the cost of simply buying a new vehicle? Only time will tell.

Electric Concept Cars
Over the past several decades, a number of electric concept cars have been developed. Some, like the Electrovair II and the Electrovette, never made it to the showroom floor, while others on this list may have a fighting chance. Here's a short list of EV concept cars and the batteries that power them:
1966 Electrovair II (General Motors) silver-zinc batteries
1976 Electrovette (General Motors) lead-acid batteries
2005 Volvo 3CC (Volvo) lithium-ion batteries
2007 Chevy Volt (General Motors) lithium-ion batteries
2007 Nissan Mixim (Nissan) lithium-ion batteries
2008 Continental DC (Bentley Motors) lead-acid batteries
2008 Subaru Stella (Subaru) lithium-ion batteries
2008 Nissan Denki Cube (Nissan) lithium-ion batteries


Lots More Information

Related HowStuffWorks Articles

More Great Links


  • Baker, David R. "Hyatt puts Tesla roadster recharging stations in 3 hotels." SFGate.
    August 30, 2007.
  • Buchmann, Isidor. "Is lithium-ion the ideal battery?" Battery University. November 2006.
  • Buchmann, Isidor. "What's the best battery?" Battery University. November 2006.
  • Doggett, Scott. "Renault Nissan Alliance Getting Recharging Stations in Place for an EV World." Green Car Advisor. July 10, 2008.
  • Elfalan, Jonathan. "First Drive: 2008 Tesla Roadster." Road and Track. March 2008.
  • Fehrenbacher, Katie. "Epyon: 10-Minute Electric Car Charging." Earth2Tech. June 19th, 2008.
  • Rodriguez, Bob. "Alternate Fuel Technology - Battery Electric Vehicles." ASE Blue Seal Tech News. June 28, 2001.