3 Reasons Why Prius 12V Battery Not Charging

Your Prius has a 12V battery, but it is not charging anymore. There are a few reasons causing the battery to not charge. The reasons are a faulty connection between the traction battery and the 12V battery, the battery sensor being faulty, the connection being loose or the 12V battery needing to be replaced.

My Prius’ 12V Battery Won’t Charge! What Is Going On?

Your Prius works like a dream. Not only do you save money on gasoline, but you also drive farther on the same tank of gas. But now you have an issue that prevents your 12V battery. What would cause the battery to stop charging?

The Traction Battery Is Not Charging The 12V Battery

Both batteries in the Prius need to keep their charges in order to operate correctly. When the charge in the 12V drops, the traction battery jumps into action and charges it. But what if the connection between the traction battery and the 12V battery is not working? Then the 12V battery will not charge.

If the traction battery is not charging the 12v battery, then it could be an issue with the 12v battery.

The Connection Cable is loose

There are several cables that connect the 12v battery to other components around the engine and the vehicle. It is possible that the cable that connects the 12v battery to the traction battery became loose, other regular wear and tear or you were in an accident recently.

The battery Sensor Is Not Working

Vehicles have sensors all around as many components to provide information to the vehicle’s computer system. The sensor that connects to the 12v battery and informs the computer system that it needs charging may have become damaged or broken.

What Is the Purpose of the 12V Battery?

As you may or may not know, the 12V battery is not used to power the engine and the key systems in the Prius. The purpose of the 12V battery is to activate and power the pre-system that does not require engine power. Without the 12V battery, the engine will not start. But after the engine is on, it is the main battery that powers lights, computer systems, A/C, etc. 

Beware Of the Error Code P3001

Whenever there is an issue with our vehicles, including the Prius, the computer system will use the senses to find out what is wrong with the vehicle. When the computer discovers the issue, it will either turn on a warning light or it will display an error code. Issues that involve the 12v battery will display the error code P3001. 

This error code signifies that something is wrong with the ECU or the electronic control unit. It could be the reason the 12v battery is no longer charging. The ECU controls the information flow between the sensors, parts around the vehicle, and the computer system. Perhaps the ECU is malfunctioning, so it is not telling the traction battery to recharge the 12v battery.

Replace the 12V battery

If you cannot charge the 12V battery anymore, then it is time to replace the battery. The cost to replace the 12V battery in a Prius is between $210 and $260. 

If your Prius is brand new, it might still be under its warranty. The warranty for a 12V battery in a Prius last about 18 months from the original purchase. Once the warranty is over, you cannot extend the warranty. 

How to Care For a 12V Battery

Here are a few tips to protect the health of your vehicle’s 12V battery and make it last as long as possible. 

Wipe the battery occasionally and whenever you see dirt and grime around the battery. If you drove through a sand or dust storm recently, take your Prius to your mechanic so they can flush or blow out the grime and dirt. Wipe the terminal and any cable around the battery as well.

When replacing an old battery with a new battery, the new battery should have a full charge. Test the new battery and ensure it has its proper charge before installing it.

Watch the temperature of the battery. If the battery gets too hot or too cold, the battery’s performance will drop.

How to Jump the 12V battery

Jumpstarting a Prius dead 12V battery is nearly the same as jumpstarting a regular vehicle’s battery. 

• Place the assisting vehicles close to the hood of the Prius. 
• Make sure both vehicles are off. 
• Connect the positive terminals on both vehicles first and then connect the negative terminals. Do not place both cables on one vehicle and then place the other set of cables on the other vehicle. The corresponding terminals must go first.
• Turn on the assisting vehicle and allow the vehicle to charge the 12V battery for 5 minutes. READY should appear on the dashboard when the battery is fully charged.

Jump starting the battery with cables should charge the 12v about it to at least 80%. If the battery does not reach 80%, then it is old. Also, if the battery reaches 80%, but the charge dropped throughout the week, then there is something wrong with the 12v battery.

Conclusion

If you see the error code P3001, then there is an issue with the ECU that is preventing the 12v battery from charging. Never charge the battery up to its full capacity. The connection cable between the traction battery and the 12v battery may have loosened and reconnecting it should fix the issue. If the 12v battery is old, then it needs replacing. If you need to jumpstart the battery, place the positive cables on the positive terminals for each vehicle first, then attach the negative cables for each vehicle. Take care of both the traction battery and the 12v battery by avoiding situations with high and low temperatures.