What a range extended electric car is

A range extended electric car (often called a REEV or range extender) runs on a battery and electric motor like a regular electric car, but it also has a small gas engine inside. The gas engine does not power the wheels directly. Instead, it kicks in when the battery gets low and generates electricity to keep the car running. You drive it like an electric car most of the time — plug it in at home or at a charger — but the gas engine gives you a backup when you cannot reach a charger.

The difference between a range extender and a hybrid is important. In a hybrid, the gas engine and electric motor both power the wheels, and they work together. In a range extender, the gas engine only makes electricity; the wheels only take power from the battery and electric motor. That means you get the smooth, quiet electric driving experience most of the time, with the security of gas as a fallback.

Key Takeaways

  • Range extended electric cars run on battery power for daily driving and use a small gas engine to generate electricity only when the battery runs low.
  • Most range extenders can travel 25 to 50 miles on battery alone, which covers the average daily commute without using gas at all.
  • You pay more upfront than a regular electric car but less than a plug-in hybrid, and you save on gas if your daily driving stays within the battery range.
  • The gas engine adds weight and takes up trunk space, and you still need to maintain it even if you rarely use it.
  • Range extenders are most useful if you have a place to charge at home but take occasional longer trips where charging stations are scarce.

How the battery and gas engine work together

When you start a range extended electric car with a full battery, it draws power from the battery to run the electric motor. The car will run on battery alone until the charge drops to a set level — usually around 20 to 30 percent. At that point, the gas engine starts automatically and runs a generator that produces electricity. That electricity charges the battery while you drive, so the battery level stays steady and the motor keeps running.

You do not feel the gas engine start in most modern range extenders; it happens quietly in the background. The engine runs at a constant, efficient speed rather than speeding up and slowing down like in a regular car, which means it uses less fuel and produces fewer emissions than a traditional gas engine would.

Once you plug in and charge the battery again, the gas engine shuts off and stays off until the battery runs low again. If you drive short distances and charge every night, you may never use the gas engine at all.

Real-world driving range and battery size

Most range extended electric cars have a battery that gives them 25 to 50 miles of all-electric range before the gas engine starts. The BMW i3 with range extender, one of the longest-running models, offers about 42 miles of electric range. The Chevrolet Volt (discontinued in 2019 but still common used) offered 53 miles. The exact range depends on the model, your driving style, weather, and terrain.

The gas engine then extends your total range significantly. A range extender with a 50-mile electric range and a 10-gallon gas tank can typically travel another 300 to 400 miles once the gas engine engages, depending on fuel economy. That means you can take a long road trip without stopping to charge, as long as you can find a gas station.

For most people, the electric-only range is enough for a daily commute. The U.S. Department of Transportation reports that the average one-way commute is under 20 miles, so many drivers would use only battery power on workdays and charge overnight.

Upfront cost and fuel savings

Range extended electric cars cost more than a regular gas car or a standard electric car, but the price varies by model and year. Used range extenders are often cheaper than new ones and may offer better value if you are not concerned about the latest technology. The BMW i3 with range extender, for example, costs significantly less on the used market than when new.

Your fuel savings depend on how much you drive on battery versus gas. If your daily commute is 30 miles and you charge at home every night, you might use almost no gas during the week. Over a year, that could save you hundreds of dollars compared to a gas-only car. However, if you take frequent long trips, you will use the gas engine more often and see smaller savings.

You should also factor in electricity costs. Charging at home typically costs less per mile than buying gas, but the exact amount depends on your local electricity rates. In most of the U.S., charging costs between 3 and 5 cents per mile, while gas costs 8 to 12 cents per mile.

Maintenance and reliability concerns

A range extender adds complexity to a car. You have a battery system, an electric motor, a gas engine, and a generator all working together. That means more parts that can fail, and repairs can be expensive if something goes wrong with the battery or the generator. However, because the gas engine runs at a steady speed and does not power the wheels directly, it typically experiences less wear than a traditional engine.

You still need to maintain the gas engine even if you rarely use it. That means regular oil changes, spark plug replacements, and fuel system checks. If the range extender sits unused for months, the gas can degrade, and you may need to add fuel stabilizer or run the engine periodically to keep it in working order.

Battery degradation is another consideration. Like all electric car batteries, the range extender battery will lose capacity over time. Most manufacturers warrant the battery for 8 to 10 years or 100,000 miles, but degradation can begin earlier in hot climates or with frequent fast charging.

When a range extender makes sense for your situation

A range extender is most useful if you have a predictable daily commute under 50 miles and a place to charge at home, but you also take occasional longer trips. You get the low operating costs and quiet driving of an electric car for everyday use, plus the security of a gas engine for road trips without the complexity of a plug-in hybrid.

A range extender is less useful if you live in an apartment with no charging access, because you would rely on the gas engine more often and lose the main advantage. It is also less useful if you have a very short commute (under 15 miles) and rarely drive far, because a regular electric car would be simpler and cheaper. And it may not be the best choice if you drive in a region with many public fast chargers, because you could use those instead of carrying a gas engine.

Range extended cars are becoming harder to find. Most manufacturers have shifted toward pure electric cars or plug-in hybrids. The BMW i3 with range extender is one of the few still in production, though used models from earlier years are available in many markets.

Range extender versus plug-in hybrid versus pure electric

A pure electric car has only a battery and motor. It costs less than a range extender, is simpler to maintain, and produces zero emissions while driving. The trade-off is that you must charge it regularly and plan longer trips around charger locations. It works best if you have home charging and most of your driving is local.

A plug-in hybrid has a larger gas engine and a smaller battery. It can run on gas alone if the battery is empty, so you never get stranded. The gas engine can power the wheels directly, which makes the car heavier and more complex. Plug-in hybrids are more common than range extenders and often cost less, but they produce more emissions when the gas engine runs because it powers the wheels directly rather than just generating electricity.

A range extender sits between the two. It is simpler than a plug-in hybrid because the gas engine only generates electricity, but it is more complex than a pure electric car. It costs more than a pure electric car but often less than a plug-in hybrid. It produces fewer emissions than a plug-in hybrid when using gas, but it is heavier and takes up more trunk space than a pure electric car.

Frequently Asked Questions

Can I drive a range extender on gas only if I never charge it?

Technically yes, but you would lose most of the benefit. The battery would drain quickly, and the gas engine would run constantly to recharge it, which uses more fuel than a regular gas car. Range extenders are designed to be charged regularly so the battery handles most of your driving and the gas engine is a backup, not the primary power source.

How long does it take to charge the battery?

Charging time depends on the charger and battery size. A Level 1 charger (standard household outlet) takes 8 to 12 hours for a full charge. A Level 2 charger (240-volt home or public charger) takes 3 to 6 hours. DC fast charging is not common for range extenders because the batteries are smaller than in pure electric cars, so it is usually not worth the infrastructure cost.

What happens if the gas engine fails?

If the gas engine breaks down, you can still drive on battery power alone, just like a regular electric car. You will have the full electric range available, so you can reach a charger or a repair shop. This is actually an advantage over a plug-in hybrid, where a gas engine failure leaves you with only the small battery.

Do range extenders work in cold weather?

Cold weather reduces battery range in any electric car, including range extenders. You might lose 20 to 40 percent of your electric range in freezing temperatures. The gas engine will kick in sooner, so you will use more gas in winter. Preheating the car while it is plugged in can help preserve battery range.

Are range extenders cheaper to insure than regular electric cars?

Insurance costs depend on the specific model, your location, and your driving history, not just the powertrain type. Some range extenders are older models with lower values, which can mean lower insurance premiums. Others are newer luxury vehicles with higher premiums. Contact an insurance company for a quote on the specific car you are considering.