What electricity actually does in a new car

Every new car—whether it runs on petrol, diesel, or batteries—uses electricity to start the engine, power the lights, run the air conditioning, and operate the computer systems that control how it drives. In a traditional car, a small battery (usually 12 volts) stores just enough charge to crank the engine over, and then an alternator powered by the running engine recharges that battery continuously. In an electric car, the battery is the engine: it stores electrical energy in cells, and that energy drives an electric motor instead of burning fuel.

The difference is scale and purpose. A petrol car's battery is roughly the size of a toolbox and holds enough energy to start the engine once or twice. An electric car's battery pack is the size of a large suitcase or bigger, weighs hundreds of kilograms, and holds enough energy to move the car 200 to 400 kilometres on a single charge. That battery is the most expensive single component in an electric car—often 30 to 40 percent of the total cost—and understanding how it works and how to care for it directly affects how long the car lasts and what it costs you to own.

Key Takeaways

  • Electric car batteries store electrical energy in rechargeable cells and power an electric motor; they are not the same as the small 12-volt battery in a petrol car.
  • Battery capacity is measured in kilowatt-hours (kWh), and a larger capacity means longer range between charges but also higher upfront cost.
  • Charging speed depends on the charger type: home chargers add 10 to 50 kilometres of range per hour, while public fast chargers can add 200 kilometres in 20 to 30 minutes.
  • Battery degradation is normal and gradual; most electric cars retain 80 to 90 percent of their original capacity after eight to ten years of typical use.
  • Cold weather reduces range and charging speed because the battery works less efficiently when cold, but the battery itself is not permanently damaged.

How battery capacity and range connect to real driving

Battery capacity is measured in kilowatt-hours (kWh), a unit of electrical energy. A small electric car might have a 40 kWh battery; a larger one might have 75 or 100 kWh. The bigger the battery, the more energy it can store and the farther the car can travel on one charge. A 40 kWh battery typically gives a range of 250 to 300 kilometres; a 100 kWh battery might give 400 to 500 kilometres. The trade-off is cost: a larger battery adds thousands to the purchase price and takes longer to charge fully.

Range also depends on how you drive. Motorway driving at high speed uses more energy than city driving with frequent stops, because the motor works harder to overcome wind resistance at speed. Cold weather reduces range by 20 to 40 percent because the battery is less efficient when cold and the car uses energy to heat the cabin. Towing or carrying heavy loads also cuts range. When a manufacturer states a range—say, 400 kilometres—that is measured under controlled test conditions, not real-world driving. Plan for 20 to 30 percent less in winter or on motorways.

Charging at home versus public chargers

A home charger (also called a wallbox) plugs into your household electricity supply and charges the car overnight or during the day. A standard 7 kW home charger adds roughly 40 to 50 kilometres of range per hour of charging. A faster 11 or 22 kW home charger can add more, but requires a dedicated circuit and professional installation. Charging at home is convenient and cheap—electricity costs roughly one-third to one-half what petrol costs per kilometre—but it is slow. If your battery is nearly empty, a full charge takes 8 to 12 hours on a standard charger.

Public chargers come in two types. AC chargers at car parks and shopping centres work like home chargers but faster (up to 22 kW), adding 100 to 150 kilometres in an hour. DC fast chargers at motorway service stations and dedicated charging hubs bypass the car's onboard charger and feed power directly to the battery at 50 to 350 kW, adding 200 to 300 kilometres in 20 to 30 minutes. Fast charging is useful for long trips but is more expensive per kilometre than home charging. Most owners do 80 percent of their charging at home and use public chargers only for longer journeys.

Battery degradation and what happens over time

All rechargeable batteries lose capacity gradually. After eight to ten years of typical use, an electric car battery usually retains 80 to 90 percent of its original capacity. That means a car that originally had 400 kilometres of range might have 320 to 360 kilometres. The degradation is not sudden; it happens slowly over thousands of charge cycles. Most owners do not notice it year to year because the loss is only a few percent per year.

Several factors speed up degradation. Repeatedly charging to 100 percent or discharging to near zero stresses the battery more than keeping it between 20 and 80 percent. Exposure to high heat—either from hot climates or from repeated fast charging—also accelerates wear. Most electric cars have battery management systems that limit charging speed when the battery is hot and prevent overcharging, so the car itself protects the battery to some extent. If you charge at home most of the time and avoid leaving the car in direct sun for weeks, degradation will be slower than if you fast-charge every day in a hot climate.

How cold weather affects range and charging

Cold weather is the biggest short-term hit to electric car range. In temperatures below 5°C, range typically drops 20 to 40 percent because the battery chemistry works less efficiently when cold and the car uses energy to heat the cabin and battery. A car with 400 kilometres of range in summer might have only 240 to 320 kilometres in winter. The good news is that this loss is temporary and reversible: as the battery warms up during driving or charging, range returns to normal.

Charging is also slower in cold weather. A fast charger might deliver only 50 to 70 percent of its rated power when the battery is very cold. Many electric cars have a pre-conditioning feature that warms the battery before you charge, which speeds up charging in winter. Parking in a garage or under cover helps keep the battery warmer overnight. Cold weather does not permanently damage the battery, but it does mean you need to plan for longer charging times and shorter range during winter months.

The 12-volt battery and other electrical systems

Even though an electric car is powered by a large rechargeable battery, it still has a small 12-volt battery like a petrol car. This battery powers the lights, wipers, door locks, and computer systems. In an electric car, a device called a DC-DC converter takes power from the main battery pack and steps it down to 12 volts to keep the small battery charged. If the main battery is completely flat, the 12-volt battery can still unlock the doors and power emergency lights.

The 12-volt battery in an electric car lasts longer than in a petrol car because it is not being drained by engine cranking and is constantly being topped up by the DC-DC converter. However, if you leave the car parked for weeks without charging, the 12-volt battery can eventually run flat. Most electric cars have a low-voltage warning system that alerts you if the 12-volt battery is weak, and you can recharge it by plugging in the main charger.

Regenerative braking and how it extends range

When you brake in an electric car, the electric motor reverses and acts as a generator, converting the energy of the moving car back into electrical energy and storing it in the battery. This is called regenerative braking, and it is one reason electric cars are more efficient than petrol cars. In city driving with frequent stops, regenerative braking can recover 15 to 25 percent of the energy you would otherwise lose as heat in the brakes.

Regenerative braking is automatic and requires no action from you. Some cars let you adjust how strong the regeneration is—a stronger setting means more energy recovery but also more noticeable slowing when you lift off the accelerator. On motorways at constant speed, regenerative braking does little because you are not braking often. In hilly terrain, regenerative braking is especially useful because the car recovers energy every time it goes downhill. Over a year of typical driving, regenerative braking can add 10 to 20 percent to your effective range compared to a car without it.

Frequently Asked Questions

Does an electric car battery need to be replaced after a certain number of years?

Not usually. Most electric car batteries are designed to last the life of the car, typically 10 to 15 years or more. Degradation is gradual, and even after eight years, most batteries retain 80 to 90 percent of capacity. Battery replacement is expensive—often £5,000 to £15,000 depending on the car—but it is rarely needed during the ownership period of most drivers.

Can I charge an electric car in the rain or during a thunderstorm?

Yes, it is safe. Electric car chargers have multiple safety systems including ground fault detection and waterproofing. The charging connector is designed so that live contacts are only exposed when fully inserted into the car. Charging during rain or light storms is not a risk, though it is sensible to avoid charging during severe lightning storms, just as you would not want to be outside in one.

What happens if the battery runs completely flat while I am driving?

The car will not suddenly stop. As the battery depletes, the car's display shows the remaining range, and the motor gradually loses power. You will have time to reach a charger or pull over safely. Most electric cars have a buffer of a few percent that you cannot access, so the battery never truly reaches zero while driving. If you do run out of charge, the car can be towed to a charger or charged on-site by a mobile charging service.

Is it bad to leave an electric car plugged in overnight?

No. Modern electric cars have charging management systems that stop charging once the battery reaches your set limit (usually 80 percent for daily use) and then maintain that level. Leaving the car plugged in overnight is actually good practice because it keeps the battery topped up and ready for the next day without requiring a full charge cycle.

Do electric cars lose charge when parked for a long time?

Very slowly. A parked electric car loses roughly 1 to 3 percent of its charge per month due to the 12-volt battery and computer systems drawing small amounts of power. If you park for several months without charging, the battery will be noticeably lower when you return. Most owners plug in once a month during long storage to keep the battery healthy and the 12-volt system charged.