I want to alert everyone of an issue with the auxiliary 12 volts battery in the new Prius prime 2024

No, they only use the GR8 diagnostic/charger. Researching the GR8, apparently most dealerships use this because it provides a receipt-like “ticket” that allows them to submit a warranty claim.

According to the owner’s manual, there is a criteria related to the “20 hour rate capacity”; if it is low, “even if the time period where the vehicle is not used is a short time, the 12-volt battery may discharge and the hybrid system may not be able to start.”

In my case, I drove the car on Sunday afternoon and it failed to start on Wednesday morning.

Reading about this problem here and elsewhere, why aren’t owners making a big protest back to Toyota? I’m planning to contact Toyota, Consumer’s Report, and Motor Trend. Motor Trend should be made aware of this issue with their 2024 Car of the Year!

 

Just found this in the owner’s manual. After I last drove the car, it was put on the charger when we got home and I left it overnight since it wasn’t going to be completely charged until 11:30 PM. Removed the charging system at ~8:30 AM the next morning and didn’t try driving it until two days later.

 

if you don't drive too often you might need a maintainer

 

The dealer texted me this afternoon that they tried to start the car and it didn’t work, a day after they said everything had checked out ok. Very glad that I didn’t listen to them to pick it up yesterday!

I asked them to see if a larger capacity battery, such as the Truestart 470CCA mentioned by another poster, could be installed. I also bought the NOCO GB40 battery booster in case this happens again…

 

I believe the 12 volt is an AGM battery.

 

Somebody's gotta do a phantom load test. It's not hard; might get to the bottom of this. It could be excessive phantom load, or the hybrid battery charging causing excessive draw, or a combo of the two.

 

Ok so the battery issue just reared its ugly head. Have a 2023 for about 1 year, battery dead this week. Toyota roadside boosted it, dead again 3 days later. Replaced battery by Toyota (supposedly bad battery as it failed the tests)

I’m fairly sure I did everything correctly with the battery as per best practices and it still died.

 

does canada have the software tsb? don't count on the dealer to know.

 

Did you check to see if you have a tracker tied into your OBD port under the dash?

 

Not on the '23-24 Prius models.

Conventional flooded lead acid 12v battery.

 

Did anyone post the TSB number or document for this? I looked but couldn't find it

 

I believe that's referring to this, issued this month:

T-SB-0054-24
12V Auxiliary Battery Charge May Deplete When PHEV Charging Cable has an Extended Connection Without Charging

From here:

Parasitic battery drain? | Page 4 | PriusChat

 

No OTA fix.

https://attachments.priuschat.com/attachment-files/2024/06/251649_T-SB-0054-24.pdf

 

Today was my turn to have a dead aux 12 volt battery. Car is 2024 Prime XSE Premium 6 months old with 3600 miles. No READY light when going to use car. Unusual feel to brake pedal when pressed. It pushed back firmly. Lights flashing etc and knew it was a battery issue. Installed jump pack on under hood connections to power car up. Fortunately jump pack I was able to reach in trunk area and was NOT stored beneath platform.

I have a Topdon battery charger/tester which showed about 6.7 volts. Could not do a test of battery since it was under 8 volts. Called dealer for appointment and confirmed they had battery in stock.

With battery charger hooked up, the voltage started to increase and the battery charge a e up. After a few hours on the charger, I ran the battery test and it came back good battery with CCA higher than the 285 that the battery is rated for. Disconnected the charger, powered car up and got READY indication. With a voltmeter, measured about 13.9 VDC at terminals so the charging system is functional. Called dealer to cancel appointment for now.

I do to drive short trips with a long one being less than 20 minutes.

I have an amp clamp meter that measures DC amps. Put the amp clamp on the battery negative cable with a voltmeter on the battery terminals. Installed a light in the baggage compartment so I could read the values with the lift gate closed.

With all doors closed, the driver display blank and dome light off, the amp reading was 2.5 amps for @ 4 minutes and voltage @ 12.5 VDC. With time the amp reading decreased and the voltage increased. After 12 minutes, the amp reading was @ .28 amps with 12.7 VDC. Both meters auto shutdown so that was the end of this very preliminary testing.

I was surprised at the amount of current draw from the battery. No surprise if doing short trips the battery would probably not sufficiently charge.

I’m hoping to perform a more comprehensive test. Probably disconnect the negative lead and install an amp meter in series for better accuracy plus disable auto shutdown on the meters.

With the number of reports in this forum for a relatively small sample size of 2023-2024 Prime vehicles, seems Toyota has a problem that needs engineering investigation. I don’t leave the charger cable in. Typically disconnect when get notification battery is charged.

Cheers

 

These gadgets allow gathering data more easily. There are many kinds and the shunt type that can measure amps. At the least it will notify the soc and amps in real time and store the data for five days. Should never have to find the battery unable to start the car again.
Search Amazon fir battery monitor. A couple I have are the bm200. Link doesn’t post.

 

toyota doesn't have a problem, their customers do. if you don't drive enough to keep it charged, install a pigtail to the battery or jump point and keep it on a maintainer.

 

Just like how the iPhone was held wrong.

 

Steve knew his time was limited, Toyota still has time to put out a fix, but will they?