5 Major Prius Hybrid Battery Failure Symptoms (And A Few Minor Ones)

The Toyota Prius hybrid car has been a game-changer since the first day it entered the automotive world. Having both an electric motor and a gasoline engine, the vehicle offers drivers the best of both worlds.

Still, unlike a regular combustion-engine car, the batteries in a Prius do fail after being in use for quite some time.

Five significant signs that the Prius hybrid battery is failing include.

1. A loss in fuel economy.
2. State of charge problems.
3. Not holding a charge for long.
4. The combustion engine runs more often than it should.
5. Some unusual engine noises.

In this article, we’re going to take a deep dive into those five significant signs that the Prius’ hybrid battery is failing.

Then, we’ll even look at some more minor signs that you can use to diagnose whether or not your Prius batteries are due for a replacement.

Let’s get started.

Major Signs That Your Prius Hybrid Battery Is Failing

Here are five of the major battery failure symptoms that you might experience with your Prius hybrid car.

Worse Fuel Economy

For most people, one of the main reasons for wanting to own a Prius in the first place is the excellent fuel economy.

Thanks to the combination of a gasoline engine and an electric motor, a Prius can go for many more miles on a regular tank of gas.

So, when you start to notice that the once-fantastic fuel economy of your Prius starts to become less so, that could be one sign that the car’s batteries are slowly reaching the end of its life.

But why is that so?

Well, it’s pretty straightforward. You see, if the Prius’ batteries were in good shape and retaining their charge like they should, then they’ll have no problems providing the electric motor with continual energy.

To put it simply, having healthy batteries in your Prius means you’ll be able to go more miles without having to switch over to the gas engine.

However, suppose the Prius’ batteries were not working as efficiently as before.

In that case, the car will end up utilising the gas engine more often. As a result, it’ll consume more of the gasoline in its tank faster than usual.

So, when your Prius ends up consuming more gasoline than usual, that’s usually a significant symptom of battery failure.

State of Charge Problems

Another term that you’ll hear often is ‘state of charge’. To put it simply, that refers to the indicator of how charge remains in your Prius’ batteries.

You’ll usually find the state of charge indicator displayed inside the Prius, somewhere on the centre console.

When the batteries in your Prius are fully charged, the indicator should show that they are at 100%.

As you drive around and the batteries’ energy depletes, the state of charge will also go down to reflect that status.

Suppose your Prius’ batteries are gradually failing. If that’s the case, you may notice problems with their state of charge.

For example, the car may indicate that the batteries are fully charged one moment but lose half or more of its charge just a few minutes later.

Besides that, you may also notice that the state of charge increases as well.

These erratic changes in the state of charge are a clear symptom of battery failure in your Prius hybrid, as it wouldn’t happen in a car with well-functioning batteries.

Battery Can’t Hold A Charge

Another clear sign that your Prius’ batteries aren’t working so well anymore is that they can’t hold a charge.

In simpler terms, that means that they lose energy even when they’re supposed to be fully charged.

For example, imagine if you hopped in your Prius first thing in the morning to drive to work.

Typically, the car’s battery should still be fully charged. Yet, you notice that the battery is at 75% or even less.

When a battery loses its ability to hold a full charge, its health isn’t as good as it used to be.

If you continue using the same battery, it will continue to lose even more of its ability to hold a full charge.

Eventually, the only thing that you can do is replace the car’s battery entirely.

The Combustion Engine Runs Often

Being a hybrid vehicle, the Prius will rely primarily on its electric motor and switch over to its gas engine only when necessary.

If you’ve been driving your Prius for a long enough time, you should be familiar with how often the combustion engine kicks on and takes over.

Suppose you notice that the gas engine gets used more often than it used to. That’s a clear symptom of battery failure.

Simply put, the car cannot draw enough energy from those batteries to power the electric motor.

As a result, it has no choice but to switch over to using the combustion engine instead, powered by the fuel from the gas tank.

Just as you might expect, this will happen increasingly often as the batteries continue to deteriorate further.

So, it’s best to replace the Prius’ batteries when you notice this is becoming a common occurrence.

Unusual Engine Noises

As you’ve seen from a few previous points, a clear-cut symptom of battery failure in the Prius is when the car relies on its combustion engine more often than it should.

The longer that happens, the more your combustion engine will experience increased wear and tear.

That can also lead to secondary effects or symptoms, such as problems with the combustion engine.

Suppose you let this continue for an extended period. As a result, the gas engine may start to develop problems of its own, and it may even end up making unusual noises.

Remember: as your Prius’ batteries continue to fail and it relies on the combustion engine more and more, your car essentially becomes just like any other conventional car on the road.

That means the likelihood of engine troubles also goes up, just as they do with non-hybrid vehicles.

Additional Signs That Your Prius Hybrid Battery Is Failing

In the previous section, we explored all of the main battery failure symptoms you may experience in your Prius hybrid car.

We consider them to be the primary symptoms because they’re easy to notice, even without any additional diagnostic equipment or software.

Still, there are several additional signs that your Prius hybrid battery is failing. For some of these other symptoms, you’ll require an aftermarket mobile app that provides you with diagnostic information about your car.

Typically, they include a mobile app that’s compatible with an onboard diagnostics (OBD) adapter that plugs directly into the car.

That OBD adapter or device will send critical information to your phone, so you can look for additional battery failure symptoms.

Let’s take a closer look at some of these additional hybrid battery failure symptoms that you can look out for with the help of such a device.

Batteries Are Running Too Hot

The first symptom that you’ll want to look out for is the battery temperature. You see, the batteries in your Prius are meant to operate only within an optimal range of about 77-80 degrees Fahrenheit.

A healthy battery that’s in good working condition should only measure within those temperatures, as shown through your mobile app and OBD adapter.

However, suppose your car’s batteries are starting to fail. In that case, you’ll notice that the temperature will begin to rise and go well above that optimal range.

But why do the Prius’ batteries overheat?

Well, a failing battery that can’t hold a charge will continue to recharge more often than usual.

For as long as that battery keeps recharging, its temperature will continue to be higher than usual.

Battery Voltages Are Low

Voltage levels are clear indicators of a battery’s health. That’s also another reason why onboard diagnostics (OBD) apps can be beneficial, as they’ll show you the voltage level for each battery block in your Prius.

For example, each battery block typically runs at 14 volts. Still, suppose you were to monitor the voltage of each block and notice that they’re dropping below that amount.

In that case, that’s a symptom of a battery that might be on its way towards failing.

Battery Vent Blowing Too Much

Still, there are a couple of additional battery failure symptoms that you can look out for without the use of any apps or OBD devices.

The first example is when you notice that the battery vent is blowing too much or too often.

Think back to one of the points discussed previously: a symptom of a failing hybrid battery is when it runs too hot.

Without using any onboard diagnostics, you wouldn’t be able to know whether your Prius’ batteries are heating up too much.

Thankfully, there’s an indirect method of sensing that. You see, the Prius has a vent that helps to remove hot air from around its batteries.

On a hot day, for example, that vent will blow to allow the batteries cool down.

Suppose you notice that the battery vent is blowing more often than usual, even when it’s not hot outside. If that’s the case, then that’s an indicator that your batteries are getting too hot.

Overheating batteries, as mentioned before, are a clear sign that they’re on their way out and might fail on you soon.

Check Engine Lights

Finally, don’t forget the classic sign of any troubles in a conventional or hybrid car: the check engine light. In a Toyota Prius, the check engine light might come on when your batteries are failing. 

At first glance, it might not be evident that the batteries cause that light to come on. However, you can figure that out by ruling out any other engine problems. 

So, if the check engine light comes on in your Prius but you can’t find anything wrong with the engine, then it might be that there’s a problem with the batteries instead.

What Do I Do If My Prius Hybrid Battery Is Dying?

So, suppose you’ve checked for all of the Prius hybrid battery failure symptoms mentioned above, and you’re convinced that your car’s batteries are failing. What can you do about it?

Well, generally, you have two options: you can either replace or fix that battery.

Here’s a quick look at the benefits and drawbacks of those two options.

Replacing A Prius’ Dead Battery

Common sense would tell us that a dead hybrid battery should be replaced. While many Prius owners may consider that to be the ideal solution, the truth is that a brand new battery could be far too expensive to buy.

Still, many Prius owners would consider this to be the safest and most reliable solution to a dead battery problem.

So, it all boils down to personal preference, and most importantly, personal budget.

Of course, there is the secondary option, which is to purchase a refurbished battery instead.

While still a little pricey, they’re much more affordable compared to a brand new hybrid battery for your Prius.

Repairing A Prius’ Dead Battery

Alternatively, you could also opt to repair your Prius’ dead battery instead. Yes, that’s right! Even with all of the Prius hybrid battery failure symptoms mentioned above, you can still repair that battery and get it working again.

Here, you also have two options: you can repair it yourself using guides that you can find online or find a local workshop that can do it for you.

If you’re the DIY type, then repairing it yourself might be a viable solution. However, you should only do it if you’re confident in working with batteries yourself.

If you’re unsure about it, it’s always best to leave it to a qualified technician.

Besides that, you can also find a local workshop to do it for you. With so many Prius owners out there nowadays, you can rest assured that you’re not the only one who wants to get their hybrid batteries fixed.

And wherever there’s demand, there’s always someone who will cater to that demand.