How Does a Hybrid Work?
If you open the hood of a hybrid electric vehicle (HEV), you’ll see that it looks a lot like a conventional gasoline car – because in many ways it is. You will see an engine, a transmission, a timing belt, etc. However, you’ll notice the engine is often slightly smaller. This is because HEVs use a hybrid battery to provide extra, supplementary power to the vehicle. But how does it work? To better understand, let’s explore in more detail how hybrids cars work.
There are two batteries in all HEVs: the auxiliary battery and the traction battery pack. The auxiliary battery serves the same purpose as it does in a conventional gasoline car— to supply the power to the ignition system and other accessory systems (like the radio, power windows, etc.) even while the motor isn’t running. The traction battery pack is what provides increased fuel economy and acceleration, including the full power required for low-speed acceleration.
The traction battery pack is typically made using nickel-metal hydride (NiMH) or lithium-ion batteries stacked together and located near the rear axle so that, in the case of a collision, the battery is well-protected in a fireproof metal box.
You might be wondering whether the battery is flammable or explosive. The current generation of NiMH batteries used in hybrid cars are non-explosive. Lithium-ion batteries can hold a greater charge within the same amount of physical space – but this extra charge capacity comes with a potential downside. In theory, Lithium ion batteries can be explosive under certain conditions; however, automakers and independent testing have indicated that the batteries are not dangerous because the fireproof box keeps passengers safe.
Nothing lasts forever, and batteries are no different. The lifespan of a battery can vary based on miles driven and the vehicle specs. Almost all batteries are subject to degradation with time and each vehicle has a slightly different configuration that causes the range to vary. To learn more about batteries, we have an entire section dedicated to Batteries/Range: Complete Guide to Electric Car Range & Batteries.
HEV Battery Warranty
Conventional gasoline cars have a mechanical warranty to cover major problems relating to the engine, transmission and other essential systems. Hybrid warranties are similar but on top of the mechanical protections, hybrid batteries often have their own separate warranty.
As an example, a 2020 Toyota Prius has a 10-year, 150,000-mile warranty on its battery. This warranty however is different from the mechanical warranty, which at the time of this article is an eight-year, 100,000-mile warranty.
Keep in mind that each automaker has its own set of terms and conditions for the warranty on their vehicles, so we suggest taking the time to fully understand which make and model is the right fit for you, your transportation needs and how long you intend to keep your vehicle.
Questions that often come up related to used hybrids are: what if I consider a used hybrid that no longer has the battery under warranty? If a replacement is required, what will it cost?
The battery cost will vary based on the year and model of the car. As an example, if we look at the 2010 Toyota Prius, the cost ranges from $3,000 to $5,000. While this is expensive, it’s worth mentioning that replacing batteries is the exception rather than the norm. For instance, a Prius can often go up to 300,000 miles without needing a battery replacement. The cost of batteries continues to decline as technology continues to improve.
Charging an HEV
One of the benefits of driving a PHEV over a traditional hybrid is that the battery can be charged by plugging it in.
You can further reduce your costs if you take advantage of off-peak electricity rates that may be offered by your local electric utility. Generally, charging your car during peak power consumption times (when everyone else in your area is awake and using electricity) can be much more expensive than if you were to do the same charge cycle overnight. Knowing when to charge is an important part of reducing the cost of ownership.
For a comprehensive understanding of electric car charging, read the Definitive Guide to Charging an Electric Car.
Since an HEV can’t be plugged in, the battery must rely on a process called regenerative braking to recharge. To fully understand regenerative braking, we have to step back and understand an energy principle of physics called kinetic energy. Kinetic energy is the energy of motion – and cars in motion have a lot of kinetic energy.
When you hit the brakes in a traditional vehicle, the energy is transferred from the body of the moving vehicle to the braking system, causing that kinetic energy (from the car’s motion) to turn into friction and heat energy as the vehicle is slowed. After a long drive you might notice your brakes will be hot. While effective at stopping the vehicle, that friction leads to wear and tear over time, which is why brake pads and/or rotors on any car will require eventual replacement.
The braking system on a hybrid vehicle is different from a conventional braking system. As soon as the driver lifts off the accelerator, even before the brake pedal is pushed, the system will start to harvest the energy from the car’s moving body, slowing it down. It does this by taking the mechanical energy and converting it into electrical energy. That energy is then sent to the battery to be stored where it will be used to power the vehicle later.
So, remember that friction and heat produced in a traditional car? In a hybrid, instead of being released and wasted as heat, the car holds onto the energy and uses it to recharge its battery.
Hybrids still have the same brake pads found in conventional cars, but they are secondary to the regenerative system. This is why brake pads on hybrids can last for up to 100,000 miles as regenerative braking creates a majority of the braking force. Some hybrid drivers even find that, once they get the hang of it, they can drive most of the time by only using the accelerator! (Of course, everyone needs to hit the brakes once in a while, especially when coming to a complete stop.)
Battery Energy Flow
Drivers can see first-hand the fuel economy and energy flow distributed throughout the hybrid. From first starting up the vehicle to cruising down the highway, the computer system identifies which of the various driving modes it should operate in and adjusts accordingly. This could include gas-only mode, electric-only mode, idle mode or charging mode. Many manufacturers will showcase these energy flows in real-time – either in the instrument cluster or on the center screen.
Each automaker has specific configurations, depending on the vehicle, that will engage and disengage when energy flows into or out of the battery. Understanding why and when your battery is charging up or sending energy to the wheels can be pretty interesting! And knowing when you’re using more of that precious battery power helps many drivers ease up on that gas pedal in order to be a little more eco-friendly.