Third day with new car, dead 12V battery, second day in a row :(

Dropped my '24 Prime off at the dealership today, they did find a service bulletin for something battery related, so I'll try to share that info on Monday when I have more details if it's related. They're keeping the car to monitor any drains.

 

If you got the data; I'd like to know which fuse in the gen4 and gen5 I need to pull to test if the DCM is drawing down the battery. I suspect that pulling this fuse should also give you a low battery warning.

 

You get the award for diagnosing mine.

I didn't know the dealer put an alarm on mine because I negotiated it off to get MSRP, but apparently they leave it installed but deactivated even if you don't fall for it. They said it was the drain as far as they can tell and removed it.

I did install a battery monitor and will see if leaving it plugged in drains it dead too, because that could still be going on.

 

Any opinion about the Batery Monitor drain on the battery ? Do you consider it to be excessive ?

 

My version of a battery monitor - A tail light bulb with 2 wires and alligator clips soldered on. I brought this device into a Honda Dealership that had my car for 3 days and could not find the short killing the battery. Car was under warranty - so it was in their shop.

All I did was clip the bulb in series and of course it lights up nice, because something is using current so I pull fuses till you see it cut off and go from there,.

In my case it was a short in the drivers rear tail light - water got in and it was looking like hair and penicillin once we got in there. replaced that wet socket and issue went away.

And your battery monitor is looking more precise but same principle - pull circuits till near zero draw and you should be able to nail it down and figure out who is doing it.

New car - seems like some electronic box over spec or maybe pinched wire. Good Luck and let us know what you find!

 

If it turns out to be a faulty 12volt, and not something with the car, you may be facing an indefinite backorder for the replacement. Insist that the dealer at least provide a different battery until they come back in stock. It's the absolute least they could do.
My battery failed and the dealer would easily still have my car if I hadn't visited in person and escalated it to the parts/service manager.

Also, if you use roadside assistance to jumpstart in the future, be absolutely 100% sure they know how to jump it right. Tow driver destroyed a couple fuses on my car when he jumped it backwards - 1k repair bill and weeklong wait.

 

I'll post when I have numbers. I plan to trickle charge the 12V full overnight, then attach the PHEV charger (with the traction battery full) and monitor any draw for 2-3 days.

 

I have an anti theft system in my car that was installed, similar to lojack in that it has GPS trackers installed. But the system I use, which is recommended by my insurer (and which comes with a cash back on installation for certain high theft makes and models like the highlander) doesn't use the car's 12v.

As best I've come to understand they install multiple low power emitting transceivers in the car that run on I can only assume batteries, and it's warrantied to work for 5 years and if the car is unrecoverable during that contract period (all prepaid in advance) you get a 5,000 CAD payout on top of your insurance pay out if you have comprehensive.

It was 650$ plus tax here, and dropped my comprehensive coverage by 10%, saving us 120 a year on our premium. I figured, for $50 after accounting for the discount, it would be worth it. For people who own RAV4s and Highlanders (on the high theft list), they get $500 cash back on proof of installation from TD insurance for aftermarket anti theft. They put a few in the body of the car, and they also put them on some car parts including the CAT, which - supposedly - makes it even harder to sell them if they do end up stolen. Only the installer and the actual company know exactly where they were installed, so it adds to redundancy etc.

The system is called TAG, and they're based in montreal. If you're a canadian interested in this kind of thing but don't want to worry about a parasitic draw on your 12v. For me the main draw was not worrying about the 12v. Its the same reason I have a dash cam with adapter that only turns it on when the car is on. I don't want to tap the wires for "parking mode" for the issue of 12v draw (and because I don't want to chance warranty issues in the first 3 years bumper to bumper either).

 

The same 12 volt is used in numerous cars, including the Chevy Bolt. That’s what Oreilly site says about other cars it fits.

 

Well, I have joined the club of failed 12v batteries. On Friday (March 1st), my car had been parked in the garage for a bit less than 48 hours (unplugged), and I went to get in, and…. Nothing. Had to use the mechanical key to get in and still no lights, so definitely a dead 12v. I pulled out my portable 12v booster battery, but elected to call Toyota Roadside instead to make sure the failure is on the record, given the known history of this issue. The guy came and boosted the battery quickly and I was good to go.

I was due for my first maintenance on the car, so I had it at the dealer yesterday (Tuesday) to have that done, and also told them about the 12v and asked them to test the battery. So they did, and after about 20 mins the service manager came back to me to provide me an update and said it was “strange”… “the car is OFF, but the testing computer still says the battery is under LOAD”. (?). They seemed completely baffled as to why this would be - they ended up disconnecting the battery completely from the vehicle, and then the test ran, and indicated it was pushing MORE Amps than it should, and failed. Report is attached.

The recommended is to replace the battery so that was done under warranty and thankfully they had one in stock so they did it right away, so I drove away once the work was complete.

Who knows if it will recur or not, but good for now.

As mentioned previously, I do have a ScanGauge II which I used on my 2014 and was never an issue (never replaced the 12V in 9 years and 220K KM), but have not tried it with my 2023 yet, and of course was going to wait until this issue was resolved. Now, I am not sure if I want to use it yet, or wait longer to see if there is any permanent fix for this issue, assuming it was not just some defective batteries….

 

From yoir battery load test report:
"Defect: Sulfation/Degraded Voltage: 12.71 V ......."
Desulfation happens when a Lead acid flood battery is left at a low state of charge for some time, or is never recharged fully after a deep cycle discharge.
Glad they found the battery defect and replaced the battery. If the charging system in the car was working correctly, and you started the car and ran it down the road for 15-30 minutew nearly every day, the battery should not have Sulfation.

 

23 hours plugged in but not charging. Drained from 12.67v to 12.46v. I'll leave it plugged in and we'll see if it flattens out or continues until dead.




The voltage monitor exactly matches my Fluke 87 III

 

Has anyone tested the amperage in the 12 volt circuit, with the hybrid battery charge cord connected? Normal would be around 20 milliamperes.

 

Day 2 plugged in but not charging: 12.46v to 12.38v.

After reading about gen4/5 battery behavior, it seems like Toyota may have designed it to stick around 12.4v?

Could any of you please share the resting voltage of your 12v batteries? It can be random, I'm just interested in having a snapshot.

 

Mine stays around 12.2
I've been watching Car Scanner - All Sensors feature and it has two different 12 volt readings. There is one at the top of the list and another further down the list that shows the reading at the odb2 ports connection.
I open Car Scanner - Press the Prius Start Button once (foot off the brake pedal - in ACC mode ) - hit the connect button of Car Scanner - and look at both the 12 volt readings.
Next, I press the Start Button a second time - foot off the brake pedal - in ON mode -, and watch both 12 volt readings jump around between 13 and 10 volts.
Finally I press the brake pedal and press the Prius Start Button again - both 12 volt readings jump up to between 15 and 14.4 volts.

One of these days I'll take a look at what ACC and ON modes look like after a trip and see if there's a difference between a trip driven only in EV mode and one driven in HV mode.

 

Thanks for this thread. I just got a new Prime a week ago and haven't had problems starting the car but I noticed I couldn't have the radio on for 5 minutes without getting a low battery alert. My digital load tester rated it at 12.8V 266CCA which isn't far off the 285CCA printed on the battery. But after hooking up a battery charger it has been taking charge at 10A so it's apparently low. I haven't been running my radio for long, nothing hooked to OBD, no aftermarket things. But I have been leaving it on the charger and also just read about not doing that in the manual. The industry is inconsistent - Tesla wants you to leave the car on the charger, but I think Nissan also wants you to leave it unplugged. I'm going to buy one of these battery testers

and do my own tests as well.

The report says it measured 316CCA rated 285CCA so by that measure the battery is fine. I have an electronic battery load tester and that's all it can measure. Does anyone know how this Sulfation/Degraded is detected, and is there a way to do it through a home tester? I thought sulfation would manifest through a lower CCA capacity. I found a description of sulfation causes, none of which make sense in these cases.

• A battery is overcharged
• A battery is stored above 75°F
• A battery is stored without a full charge

 

Some dealers put trackers on all their inventory, and those are additional drain on the battery.

The charging standard has safety protocols that only energize the cable when actively charging(or preconditioning). When plugged in, but not actively charging, it is the 12V powering the monitors. Tesla's and others have systems in place to charge the starter battery if it gets low; might even do so when unplugged. The rest do not.

 

I have to say, after reading this topic, I'm concerned that my on-order Prime may be a mistake. I intended to plug in the car every day, with a scheduled charge daily from 2am-7am. Didn't figure on having to worry about the 12V battery every day. Are these battery issues just a tiny percentage of Prime owners? Seems odd that a 20 year old car line would have this type of serious flaw. I don't think I've ever had a dead battery in 40 years of new car ownership. Pretty disconcerting seeing it come up as an issue in 2024.