The basic design
A battery electric car replaces the fuel tank and engine with a large rechargeable battery pack and one or more electric motors. The battery supplies direct current, an electronic controller regulates how much power reaches the motor, and the motor turns the wheels. Because electric motors can deliver strong pulling force from a standstill, many electric cars accelerate smoothly. They typically have far fewer moving parts in the drivetrain than a combustion engine, so some routine maintenance items differ, although tires, brakes, suspension and cabin systems still wear.
Some vehicles are hybrids. Plug-in hybrids have both a battery you can charge and a fuel engine, while ordinary hybrids use a smaller battery that is not plugged in. This article concerns fully electric cars.
Regenerative braking
When you slow down, an electric motor can work in reverse, acting as a generator and sending some energy back into the battery. This is called regenerative braking. It recovers part of the energy that would otherwise be lost as heat in the brakes, and it is one reason electric cars can be efficient in stop-and-go traffic. It recovers only a portion, not everything.
Battery size and what kilowatt-hours mean
Battery capacity is measured in kilowatt-hours (kWh), the same unit used on electricity bills. A larger number means more stored energy. The battery chemistry is usually a lithium-ion type, and the basics of battery chemistry explain why range slowly declines over the years.
Efficiency describes how far a car travels on each unit of energy. Here is a hypothetical example. Suppose a battery holds 60 kWh of usable energy and the car averages 4 miles per kWh. Then the distance is 60 × 4 = 240 miles. If conditions worsen and efficiency drops to 3 miles per kWh, the distance becomes 60 × 3 = 180 miles. These numbers are only illustrations, not figures for any real vehicle.
What range really means
Range is the distance a car can travel on a full charge. The published figure comes from a standardized test, and the testing method differs by region, so numbers are not always comparable across sources. Real-world range varies with:
- Speed. Higher highway speeds use more energy because of air resistance.
- Temperature. Cold weather can reduce range, partly because the battery is less efficient and partly because heating the cabin uses energy. Very hot weather can also have an effect.
- Terrain. Climbing uses extra energy, though some is recovered going downhill.
- Load and tires. Heavy loads, roof racks and low tire pressure all reduce efficiency.
- Driving style. Smooth acceleration and anticipation generally help.
A practical approach is to treat the stated range as an approximate upper guide and plan around a margin. Most daily driving is relatively short, so for many people the question is less about maximum range and more about whether charging fits their routine.
How charging works
Charging is often described in levels, and the details vary by region.
- Basic home charging. Plugging into a regular household outlet is the slowest way to charge. It can be enough for people who drive short distances and park for many hours.
- Dedicated home or workplace charging. A purpose-installed charger on a higher-power circuit is much faster, often enough to refill a typical day’s use overnight. Installation should be done by a qualified electrician, and a home’s electrical capacity may matter.
- Public fast charging. Direct current chargers feed power straight into the battery and can add a large share of range in a fraction of an hour. They are useful for long trips, but are often more expensive per kWh than home charging.
Charging power is a ceiling set by both the charger and the car, so a car cannot charge faster than it is designed to accept. Charging usually slows as the battery fills, particularly above about 80 percent, so many drivers on trips stop sooner instead of waiting for a full battery. Connector types differ between regions and vehicles, which is part of the story behind charging standards.
Battery life and care
Battery packs degrade slowly with age and use, as explained in the battery chemistry article. Manufacturers often provide long warranties on batteries, but terms vary, so read them. Habits often suggested to be gentle on a battery include avoiding frequent very high or very low charge levels when it is convenient, limiting repeated fast charging, and avoiding long storage at extreme temperatures. Following the maker’s guidance is the best rule.
At the end of its life in a vehicle, a battery may still have use for stationary storage, and recycling methods are developing. How common and economical this will become is uncertain.
Cost and environmental questions
Electric cars often cost more to buy than comparable fuel cars, while running costs per mile can be lower, depending on local electricity and fuel prices and on where you charge. Comparisons depend heavily on individual circumstances, so it is better to calculate with your own numbers than to rely on generalizations. Environmental effects also depend on how local electricity is produced and on manufacturing; analyses are complex and vary by region.
Home solar and home batteries can be paired with a car in some setups, though not every combination works well or pays off.
Questions worth asking
- Where will I charge most of the time, and is that practical for me?
- How far do I drive on a typical day and on my longest regular trip?
- What connector and charging speed does the car support?
- What do the battery warranty and service options cover?
- How does cold weather affect range in my climate?
Automation features such as driver assistance are a separate topic from the electric drivetrain, and self-driving cars are not the same thing as electric cars.