You can’t browse for a new car online, visit a dealership, or even watch TV without hearing about hybrid cars, for the past 20+ years they’ve been the biggest motoring trend. 

Manufacturers claim numerous benefits, the most prominent being fuel efficiency, but what actually is a hybrid car, and how do they work?

How Do Hybrid Cars Work

The term hybrid refers to a car that uses both a traditional internal combustion engine and an electric motor for propulsion. All modern hybrids have a lithium battery pack that stores the electrical energy used by the motor.

Exactly how the engine and motor work together differs between types of hybrid, with some directly powering the wheels, and others adding power to the engine's output, retaining the traditional gearbox arrangement. 

How the batteries get charged is also something that sets the different hybrids apart. All hybrids add charge to the battery from regenerative braking to some degree, but there are also hybrids that can be charged from a charger, just like an electric car. 

Types of Hybrid Cars

As we just touched on, there are multiple different types of hybrid, each combining electric and internal combustion power in slightly different ways.

Self-Charging Hybrid

The self-charging hybrid was the first kind to be sold, with the Toyota Prius in 1999. They use only regenerative braking to charge the battery. This is energy that would otherwise be wasted when braking. Self-charging hybrids are also known as parallel or full hybrids.

To enable this, the car operates the electric motor as a generator, converting the kinetic energy into electrical energy in the form of battery charge. Early self-charging hybrids were celebrated for their incredible fuel efficiency, thanks to this principle.

Self-charging hybrids can typically drive under electric-only power at low speeds, such as when in traffic, with the engine kicking in at around 15mph.

Looking for a new motor? Check out our list of the best self-charging hybrids.

Self-Charging Hybrid Benefits

• Efficiency - without needing to carry a large battery like an electric or plug-in hybrid, self-charging hybrids can achieve excellent MPG.
• No need to charge - Self-charging hybrids do away with the need to put your car on charge or need a dedicated charging point.
• Reduced emissions - with the electric motor contributing power, the petrol engine needs to burn less fuel, resulting in lower emissions.

Self-charging Hybrid Disadvantages

• No electric-only range - plug-in hybrids often have an electric-only range, thanks to their larger battery and ability to be charged prior to starting a journey. Most self-charging hybrids don’t have an EV-only mode.
• More complex than a petrol car  - Whilst they offer higher fuel efficiency, hybrids have, in addition to the usual petrol car components, a motor, motor controller and battery that can all fail and add cost

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Plug-in Hybrid (PHEV)

Plug-in hybrids still use regenerative braking to charge the battery, but they can also be charged from a home or public charger, in a similar fashion to EVs. This enables them to use the electric motor for greater periods of time.

Many plug-in hybrids can even cover a certain distance on electric only power, this is typically around 40 miles.

Plug-in Hybrid Benefits

• Best of both worlds - If you mostly do short journeys, you can effectively use the car as an EV, but when you need to do a longer trip, you aren’t bound by the charging issues faced by EVs.
• Higher efficiency - As long as you have somewhere to charge them, plug-in hybrids can achieve an MPG figure much higher than that of other hybrids.
• Tax benefits - Plug-in hybrids that have an EV range of over 40 miles are subject to more favourable VED and Company car tax rates.

Plug-in Hybrid Disadvantages

• Weight - because they have both a petrol engine and a large battery, plug-in hybrids tend to be heavier than other car types, potentially leading to increased tyre and suspension wear.
• Higher cost - Plug-in hybrids are typically more expensive than other types of hybrid and internal combustion engine cars

Mild Hybrid

As the name suggests, a mild hybrid incorporates the basic premise of combining an electric motor with a petrol engine, but on a smaller scale. Mild hybrids have small electric motors and small batteries. 

In a mild hybrid, the electric motor cannot transfer power to the wheels, instead, it assists the engine, through the same drivetrain as a normal petrol-engined vehicle. 

Mild Hybrid Benefits

• Cheap - Because they use a small battery and electric motor, mild hybrids are typically only slightly more expensive than the conventional petrol or diesel-engined equivalent
• Increased efficiency - Whilst it’s not in the same league as a full or PHEV hybrid, mild hybrids can increase fuel economy by a meaningful margin

Mild Hybrid Disadvantages

• Not as efficient - full and plug-in hybrids can achieve much higher MPG figures
• No EV-only range - with their small batteries and motors, even if mild hybrids could power the wheels on electric power only, they would have a negligible EV range

Are All Hybrid Cars Automatic?

As the combination of motor and engine replaces the traditional gearbox and clutch arrangement, all self-charging (full) and plug-in hybrids are automatic.

However, lots of mild hybrids are available with a manual gearbox.

Do Hybrid Cars Need Charging?

Only Plug-in hybrids (PHEV) need charging, all other types of hybrid cars (self-charging/full and mild) convert otherwise wasted energy into battery charge, and cannot be charged.

Are Hybrid Cars Cheaper To Run?

With the increase in fuel economy, lower VED rates, and lower company car tax, hybrid cars are almost always cheaper to run than a comparatively sized petrol or diesel-engined car.

Which Hybrid Car Is Best?

One of the best-rated hybrids is made by the company that started it all, Toyota. The new Corolla is an excellent blend of practicality, fuel efficiency and excellent engineering, it's hard to beat.

That said, most of the other brands also making hybrids are putting out some great cars, from Renault to BMW,

Author - Joseph Law

Joseph has been writing about cars for over seven years and writing for Bumper for over two, blending his passion for automobiles with a talent for storytelling.

Joseph has written about engineering and cars for Autozilla, Komaspec, and several engineering manufacturers. When he's not writing or tinkering with one of his cars, Joseph dreams of owning an Alfa Romeo 33 Stradale.