Prius 12 Volt Battery Problems 2023 – Complete Guide

Prius 12 Volt Battery Problems

The Prius 12 volt battery problems are one of the often common issues that owners of Toyota Prius have to deal with. Toyota Prius is a hybrid type of vehicle and despite its marveling engineering designs.

Features and state-of-the-art technology are not infallible to some of the challenges some other cars are bedeviled.

We understand batteries are a primary source of electrical energy for our cars, and car engines rely on them to get started. But also, other electrical appliances and devices depend on it to get powered.

For hybrid vehicles like the Toyota Prius, lots of its features and technologies can hardly deliver their purpose for complete car optimization unless they are powered adequately.

Prius 12 volt battery details

Prius 12 Volt Battery Problems

Generally, the Toyota Prius comes with two batteries; a 12volt battery in a truck and a high voltage battery pack (200V). Unlike other vehicles, the 12-volt battery does not directly start up the car engine.

Instead, it supplies the electric power to the high voltage battery pack through the boot-up of the car’s electronics that manages its engine and hybrid systems. The energy provided to the voltage-battery pack is then used to power up the engine.

The 12v is also used to power devices and car electronics even while the vehicle is off or on ready mode. And it drives us back again to the main battery because it is still the primary source of electrical energy before any other component will work independently.

The 12v battery of Prius is a sulfuric lead-acid, 46Ah and AGM type battery. Its length dimension is 9inch and width 4.3inch * 4inch. Toyota Prius 12v battery is 7.3inch in height and weighs approximately 46pounds.

Signs of a bad battery or good 12-volt battery

Before anything goes wrong, there are signs to tell you that your battery life is coming to an end or going bad. It rests on us to be observant of those crucial signs and warnings that perhaps could make us act pretty quickly before we are caught unawares.

Equally, there are significant signs to help you tell if a battery is good. Now, let’s see some of those vital signs that will help identify a good or just when the battery has gone bad:

  • Start-up; A very sound battery should start up a car without much fuss. But when it comes to a point in the battery’s life cycle where it takes too long and after many kicks to start the engine or it just wouldn’t start it after hopes that it would, the battery may be faulty. The inability to start up the car is due to the low power of the battery. That is, the battery cannot deliver the adequate energy needed to kick start the engine. This signifies that the battery is dying out and may just need a change to get the vehicle rolling again.
  • Lights; Another vital sign to note when the battery is bad is the car lighting. The car lights include both interior and exterior lights. When you observe the lights dimming each time the car is about to start and comes brightened again as the engines set rolling, there is a need to check your Prius battery as it may be going bad, if not gone already. The reasons for the dimming lights are as a result of current pulled from the supplies. This makes more power available to give the engines a start because it is insufficient to keep the lights full and start the car simultaneously.
  • Radio Preset; when you start observing the loss of your radio presets as you start the Prius engines, it is a good sign that the batteries are bad. It is no other reason than the system prioritizing power supply that temporarily cut energy that keeps the radio presets.
  • Booting Failure; when the Prius battery goes terrible, gear selections start blinking on the Odometer screen as it fails to boot into ready mode.
  • Error Message; Knowing that the Prius is a high breed car, a sudden trip off of currents from sensors of the computers could cause error messages to display on the display screen. When these error messages become too frequent even though nothing specific is wrong with the said system shown, it is a sign that our Prius 12v battery is gone bad.

Prius 12 volt battery problems and solution

problem Prius

Like we must have known before now, the Prius 12volt battery has its issues like most car batteries. However, the problems with the 12volt Prius battery are not without their respective solutions. We are going to be seeing some of these problems as well as their solutions. And it goes as follows;

1. Sudden power decline

When the Prius battery is brand new, it gives the appropriate amount of power needed to keep all functions in and out of the vehicle and starts the car engines smoothly without troubles.

But after moving the car over some mileage, the battery begins to lose power until suddenly, some car components begin to malfunction. One may wonder if it resulted from the car’s charging system, but it is because of issues with the battery that cause it not to charge as it should, causing the power in it to sap.


  • Visit a Prius Auto service expert to identify the cause precisely.
  • Take advantage of the battery’s warranty and have it fixed or replaced without extra cost.

2. Dead on Prolonged vehicle inactivity

When a Prius is left parked and unused for some period, it may become impossible to start the engines when the vehicle is about put to use again. This is not restricted to the Prius. However, when other car batteries are charged, they jump back to life and start the vehicle as expected but not for the Toyota Prius because its battery can go typically dead.


  • Keep engines running by warming up the car every day even though the vehicle is not put to use.

3. Hard to reach

The 12volt battery is located in the car’s trunk, often challenging to reach. If you happen to not know very much about the Prius battery, it may be impossible to replace the batteries on your own without the help of an expert.

This is because you are likely to do more damage in reaching the battery, affecting the car’s sensitive computer system.


  • Always seek the help of a professional when replacing batteries or trying to reach the batteries.

4. Short life span

toyota prius

Initially, the Prius battery should have a lifespan of 8-10years, but hardly does the battery gets to this projected life before it starts giving issues and, in most cases, go dead. One may wonder if something they have done wrong triggers the fault, but the problem is from the battery.


  • Talk to an expert about the problem and listen to the advice he has to offer.
  • Look through your purchase document for the warranty policy to see if you are covered.
  • Replace with new batteries.

5. Difficult to maintain

Another problem with the 12volt Prius battery is the difficulty in maintenance. The positioning of the battery makes it very discouraging to reach. And over time, corrosion starts to develop on the terminals, which could cause partial contact.

Partial contact will result in a cut in current flow, which may cause malfunctioning of the car’s hybrid systems.


  • See the manual on maintenance and follow the instructions carefully
  • Visit a certified auto service for maintenance.

Things that you need to check Prius 12 volt battery

It is very possible to check the degree of wellness or status of your Prius 12volt battery. And to do that, you need specific tools like;

  • Voltmeter
  • Cords
  • Terminal clips (positive and negative)

Step by step Prius 12 volt battery checking guide

One can check the status of the Prius battery in three ways. It can be checked directly on the battery, or we can check the battery inside the bonnet’s fuse box, just above the right tire in front. If the two mentioned methods prove too uncomfortable, we can instead check right inside the car.

Method one

Here in this method, the battery can be tested directly. Either it is tested while sitting inside the car’s trunk where it is positioned initially or brought down from the vehicle. This method is relatively straight forward and to get the battery tested;


  1. Set up the voltmeter; there is various kind of voltmeter out there. Some are analog, while others are digital. And even with the digital types, there are highly computerized ones that could give you the voltage reading and other details about the battery like the internal resistance and so on.
  2. After getting the voltage meter, set it up by plugging in the positive cord (red) and negative cord (black) on their respective positions on the meter.
  3. Identify the terminals on the battery; look carefully and note the battery’s positive terminal and the negatives.
  4. Use the clips; use clips on the voltmeter cords and place them on the battery terminal accordingly. That is, positive clips go on the positive battery head and negative clips likewise.
  5. Look to the meter screen for display; after you hit the necessary buttons, look to the display on the voltmeter screen to see details about the battery.

Method two

We can still use the voltmeter for this method, only that we won’t be testing the battery directly. Now, let’s see how to go about this test;


  1. Open the car’s bonnet; this is the first thing to do in this method. We have to open the bonnet to have access to the fuse box. Remember to keep the bonnet stable, so it doesn’t come close and hurt you in the process.
  2. Look for the fuse box; the fuse is located at the right-hand side when you open the bonnet, at the top corner.
  3. The battery’s fuse; unclip the fuse box cover gently and find the battery fuse. It is a fuse with a red cap at the top end of the fuse box. The fuse receives a direct supply of current from the battery. It sometimes comes with a plus sign on the top red cap.
  4. Place the terminals. Now, put the positive end of the voltmeter cord in the battery fuse after you have unclipped its red cap. Then place the negative end of the meter cord on a ground connection by attaching it to the car’s body. Look to the display on the voltage meter screen to see details about the battery.

Method three

The third way we can check the Prius battery is from within the car by simply hitting some buttons to display the battery details on the screen.

For some generations of Prius, you can do this by holding down on the car button on the audio display. But for others, it is not that straightforward.


  1. Hit the power button twice
  2. Hold down the car button on the audio display
  3. Turn headlights on and off (slowly) until the service menu displays
  4. Go to functions and click on settings
  5. Now, go to the vehicle signal, and you will have the details of your battery displayed.
  6. Click to go back, and when done, you can hit the power button. When you turn it on again, the display will be normal.

Battery state analysis

How to check if your Prius 12 volts battery is bad

We can run battery analysis on the Prius 12volt battery; using the battery analyzer. There are different brands of analyzers out there, but they all work on the same principle.

The analyzer can only be used on the lead-acid battery. Before seeing the steps to run the battery analysis, there is a need to review the battery analyzer’s manual for vital information. The steps to analyze the 12volt battery are as follows:

  1. Connect the analyzer’s clips to the respective heads of the battery ( positive and negatives accordingly)
  2. The analyzer has no power source and depends on the power from the battery to be analyzed. If the analyzer doesn’t come up, then there is likely hood that your battery is out of life.
  3. The first thing you will see after plugging the clips is the voltage of the battery displayed.
  4. Hit the menu button, select the preferred language option, and use the arrow buttons to navigate the interface.
  5. Select the version information and then battery information ( the info are written on the battery surface)
  6. Select battery type
  7. Select the standard, which is usually CCA
  8. Press the next button to go next page
  9. Hit the enter button
  10. Choose the position you are analyzing your battery (outside or inside the car)
  11. It will run the battery state analysis and display the results on the screen.

How to charge Toyota Prius hybrid battery

The Toyota hybrid battery is seated right in the trunk alongside the 12volt. It is the battery that actually powers the Prius engine.

Toyota Prius hybrid battery is either made of Lithium-ion or Nickel metal. Lithium-ion and Nickel-metal have their advantages as well as disadvantages.

Now let’s see how the Toyota Prius hybrid battery is charged:

  1. Cord; use the Toyota charging cord and connect to a standard electrical outlet
  2. Charge port; unlock the vehicle if it is locked and press the charge port door on the right corner panel to open. Components inside the charge port will be illuminated.
  3. Cap; remove the cap in the port and place it in the holder.
  4. Insert charger: insert the charger into the port and manipulate its head until it clicks to the position. When the charging is begun, green lights will illuminate to notify you that the battery is charging.
  5. The three blue lights; at the top of the dashboard, there are blinks on the passenger’s side to show the battery charging progress from inside the car. And when all three lights are fully illuminated, it indicates that the battery is fully charged.
  6. MID; stands for multimedia information display. On the MID, the charge status will appear and displays the amount of time it will take to fully charge the battery because the system considers the charge you are using.
  7. Standard outlet; it takes approximately five and half hours to charge the hybrid battery full when using the standard outlet.
  8. 240-volt charging station; but on the 240V charging station, it takes less than 2 and half hours.
  9. Disconnect charger; when charging is done, unplug the charger from the port and replace the cap back over the port. Close the port door and store your charging chord back to its space in the trunk of the car.

However, charging can be set manually or automatically. The manual charging is just all we have seen above. For the automatic charging, you can set it up by using the steering wheel controls to access the menu then select charge settings in the MID.

After that, select charging connector lock. You can set it as manual or automatic as you please.

With the automatic charging, you can have your charging chord automatically click to place once in the port, and it will disconnect itself when charging is complete.

Maintenance of a 12-volt battery

Maintenance is a vital routine to keep the battery life at optimum performance. The 12volt battery of the Prius can be maintained in the following ways;

  • Read and follow the manufacturer’s manual on maintenance.
  • Scrub or clean the battery terminals regularly to avoid corrosion over the battery heads.
  • Run battery analysis test periodically to see the situation of the battery
  • Replace battery after the recommended mileage


Battery state analysis

How do I prevent the battery from dying?

You can prevent your battery from dying by keeping to the maintenance guide on the manual. And also running a check on your battery regularly.

How do you know if your Prius battery is dying?

One can tell if their Prius battery is dying when they start observing their lights dimming both internally and externally, especially when starting the car. Or when the radio preset wipes off when starting the engine.

You can also tell the battery is dying when you start observing error messages displayed on the Odometer than usual. And another sign to tell your battery is dying out is the car refusing to start up when parked for some time or it suddenly goes off while driving.

Can I change the 12 volt battery even before covering the recommended mileage?

It is very possible to change the battery even before covering the specific mileage, especially when there are obvious signs of the battery dying out. But before replacing check if you have a warranty on the battery.

Is it expensive to replace a dead battery?

Well, replacing the Prius 12 volt battery may not be cheap. However, some sellers may offer better deals.

Can you give an estimate on what it will cost to replace the 12 volt battery?

It will cost between; $200-$400 to have a new replacement for your dying battery.

Please, recommend a video for me where I can watch how to run a text on my Prius battery?

There is a link to a video below, where you will be guided on how to run a test on your Prius battery.

How long does it take before the Prius hybrid battery would need a replacement?

If used as directed by the manufacturer, it will take up to 10-15years before replacement may be required for the hybrid battery.


The 12volt battery may have its short-comes. However, with a proper maintenance routine and abiding by the instructions on the user manual, we can optimize the battery’s performance.

Running checks and analysis on the battery regularly will keep us abreast of the activity going on in it. Having updated info about our battery will prevent us from being taken unawares and could help us make an adequate replacement plan when necessary.

Also, keeping to the manufacturer’s terms of usage for the hybrid battery will be best for the battery’s health and prolonged use.

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