Prius Aux Battery Low: Symptoms, Fixes And More

Have you ever had to deal with a dead car battery while in a hurry to get somewhere? It’s a common inconvenience that can derail your day, but it’s even more frustrating when it happens to your hybrid vehicle, such as the Prius. 

The Prius auxiliary battery is a vital component that powers several electrical systems in the car, and when it’s low, it can cause significant issues that can leave you stranded. 

In this article, we’ll delve into the symptoms of a Prius auxiliary battery low, how to check if it’s malfunctioning, and the steps you can take to replace it or recharge it, so you can avoid being caught off guard with a dead battery.

What Does The Auxiliary Battery Do In A Prius

The Prius is an electric car that relies on a hybrid system. 

This system operates on a dual battery system that includes a primary battery that powers the electric motor and a secondary battery that provides support to the car’s 12-volt accessories, including the parking brake securely, the headlights, the dashboard, and the backup camera. 

This second battery, also known as the auxiliary battery, is crucial to the operation of the vehicle.

Prius Auxiliary Battery Low Symptoms

Warning Lights On Dashboard

When the auxiliary battery is low, one of the primary signs is the illumination of warning lights on the dashboard. 

The low battery indicator light is the most common, but other lights may also illuminate, including the brake, ABS, or hybrid system warning lights. 

In some cases, these warning lights may even be accompanied by an audible warning or chime.

Difficulty Starting or Stalling

If the auxiliary battery is too low, the Prius may experience difficulty starting or even stall while driving. In some cases, the car may start but fail to remain running due to the low voltage. 

This symptom may indicate that the battery has lost its ability to provide the necessary voltage to start the car and keep it running.

Dim Headlights

Another common symptom of a low Prius auxiliary battery is dim headlights. When the battery is low, it may not provide enough power to keep the headlights at full brightness. 

This symptom can also affect other accessories, such as interior lights or dashboard lights.

Malfunctioning Stereo or Audio System

The Prius stereo or audio system may also malfunction if the auxiliary battery is low. This symptom may include the inability to turn on the stereo or a lack of sound from the speakers. 

In some cases, the audio system may even produce distorted or static-filled sound.

Power Window or Door Lock Malfunctions

If the auxiliary battery is low, the power windows and door locks may malfunction or operate slowly. 

These features rely on the battery to operate, and a low voltage may cause them to malfunction.

Backup Camera Malfunction

The Prius backup camera also relies on the auxiliary battery to function properly. If the battery is low, the camera may not display a clear image or fail to turn on altogether. 

This symptom can affect the driver’s ability to see what’s behind the car when backing up, creating a safety hazard.

How To Check If Your Battery Is Malfunctioning

If you suspect that your auxiliary battery is malfunctioning, you can easily check it by performing a voltage test. To do this, you will need a voltmeter. First, turn off the car and open the hood. 

Locate the battery, which is typically on the passenger side of the engine compartment. Connect the voltmeter’s red lead to the positive terminal of the battery, and the black lead to the negative terminal. 

If the voltage is less than 12 volts, then the battery is low and may need to be replaced.

What Happens If Auxiliary Battery Dies?

If the Prius auxiliary battery dies, the car will not be able to start or may stall while driving. The parking brake securely, headlights, and other 12-volt accessories may not function properly, and the hybrid system may fail. 

It’s important to replace the battery as soon as possible to avoid any further damage to the hybrid system or other electrical components.

How Do You Charge A Prius Auxiliary Battery?

Unfortunately, it’s not possible to charge a Prius auxiliary battery directly, as it’s not designed to be a rechargeable battery. 

Instead, the battery is charged by the vehicle’s hybrid system, which uses energy from the main hybrid battery to keep the auxiliary battery charged.

If you suspect that your Prius auxiliary battery is not charging properly, it may be time for a replacement. In that case, you’ll need to replace the battery with a new one. 

You can take your Prius to a certified mechanic or a dealership to get the prius aux battery replacement done correctly. 

It’s essential to ensure that the replacement battery is compatible with your Prius model and the hybrid system to avoid any further complications.

How Long Does It Take To Replace Auxiliary Battery

The time it takes to replace the Prius auxiliary battery can vary depending on the mechanic’s experience and the specific model of Prius you own. In general, the replacement process takes approximately 30 minutes to an hour. 

However, this timeframe can be longer if the replacement involves other electrical components, such as the hybrid system.


Can you jumpstart a car with an auxiliary battery?

Yes, you can jumpstart a Prius with a dead auxiliary battery using a standard set of jumper cables and another car with a charged battery.

How long does a Prius auxiliary battery last? 

A Prius auxiliary battery can last up to 4-5 years, depending on usage and maintenance.

Can an auxiliary battery be recharged? 

No, the Prius auxiliary battery is not designed to be recharged. Instead, it is charged by the hybrid system.

How do I start my Prius with low battery?

You can start a Prius with a low auxiliary battery by activating the power switch and depressing the brake pedal while holding down the gas pedal.

How much does a Prius battery cost?

The cost of a Prius battery can vary depending on the model and where you purchase it, but it typically ranges from $2,000 to $4,000.

Can the auxiliary battery drain the main battery?

No, the auxiliary battery is separate from the main hybrid battery and cannot drain it. However, a faulty auxiliary battery can cause other electrical components to malfunction, which may drain the main battery.

Final Thoughts

The Prius auxiliary battery plays a crucial role in the functioning of your hybrid vehicle. It powers important systems such as the radio, lights, and parking brake when the car is off. 

When the Prius auxiliary battery is low, it can cause several symptoms that impact the vehicle’s overall performance. Regular maintenance and prompt replacement when necessary are essential to keep your Prius running smoothly. 

With the right care and attention, you can avoid the inconvenience and expense of a dead Prius auxiliary battery. 

So always keep an eye on your vehicle and take action if you notice any signs of “Prius Aux Battery Low”.

Ricardo Vaughn
Ricardo Vaughn

Vaughn is a seasoned off-roading expert and professional winch specialist. When he's not out on the trails, he shares his knowledge and experiences through his writing as a blog author in the off-roading and outdoor lifestyle space.

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