12 volt battery failing to start the car

I’m glad I left it overnight. Battery was dead again. They are putting a new battery in. Since closed Sunday I will have to pick up on Monday.

 

My late 90’s Chrysler Town and Country minivan would deplete the 12 v. It said right in the manual don’t leave the van sit for more than 20 days. Something like that. It was true. Maintainer charged often, almost same as now, but with a much older charger. Things are on, and they use power. It isn’t a 1954 Nash.

 

I am joining the dead/unreliable 12v battery complaints. Mine started last week (March 5, 2024) and I am not even started on the path to resolution after multiple dealership visits. I wrote these notes for my own records, but I thought I’d share them here in case people want to know what they are up against with dealerships and Toyota warranty limitations.

Spoiler: background about the car and its circumstances for the first few hundred miles

Purchased a 2024 Prius Prime XSE Premium on 2024-02-08.

The car is driven regularly by a single car household with no regular commuting but plenty of local and regional travel in Colorado. For the first 700 miles, I have intentionally driven the car medium and short distances in both HV and EV modes. (My definition of a short drive is a 5 mile drive within an hour.) The car has been run on EV mode enough to not need to be fueled with more gasoline for the first 500+ miles, but it is almost due for a fill-up after the first month of ownership.

The car has definitely seen plenty of 5-80 mile drives since I’ve owned it, with no long interstate stretches but plenty of varied driving on city streets, arterial roads, and mountain roads. The car is driven 3-10 times per week, but not every single day. I rarely charge the traction battery to 100% or run it down to 0%, but I have done a few full cycles of the battery in urban driving.

The AC adapter charger is rarely left on the car after it is done charging.

The winter weather has been somewhat cold (Colorado, Zone 5 USDA scale), but only a few nights below freezing. The car is in a lightly insulated but not climate-controlled single-car garage.

No aftermarket accessories are installed, although I am trying to find out if someone has hidden a Lojack-style tracker or alarm on the car (visual checks in hidden places haven’t come up with anything, but I need proof that there isn’t one at this point).

The car runs perfectly for the first 730 miles.

2024-03-05 11:00 735 miles

12v battery is dead. Car will not start. I call Toyota Roadside Assistance to give the car a jumpstart. I had already gotten in the car to open the trunk latch manually because I had a feeling they would not be comfortable jumping from the fuse box (good guess, as they preferred to jump the 12v battery directly). At this point I’ve already read the Prius Chat forums and know the pattern of this problem.

Before the dead battery, the car had only sat for 38 hours of no use, which is the probably the longest it had been idle since I purchased it. No interior or exterior lights are ever left on as the car is always locked and garaged when not in use. ACC mode was not used extensively (I generally run the car in READY or turn it off).

After jumping the 12v battery, the car boots up immediately and there are no warning messages or any issues while driving. I drive the car to the dealership without an appointment because I want them to diagnose the issue right away.

2024-03-06 9:00 735-750 miles

The car is left at the dealership overnight to diagnose any battery or electrical issues. As far as I can tell from their notes, they only check the battery. The battery checks out fine, and the car is able to start in the morning (18 hours idle, no distance driven).

The service advisor says that the car was left on by me (“maybe”, their phrasing), with no evidence and no acknowledgment that this shouldn’t be happening on a new car after a couple of days of sitting in a garage. Maybe it’s the battery, or maybe it’s something else, but they haven’t identified the problem or spent enough time on it to properly diagnose it.

I say that I don’t want to be back in a few days with a dead battery, as I don’t have confidence that they have finished diagnosing the problem. They say they are extremely confident that I will not be back with the same problem.

I stop by an auto parts shop and check the battery and it’s reading nominal “80%” and “healthy”, which makes sense after 30 minutes driving it around town. Maybe it’s not the battery, but I have to double-check the dealer diagnosis.

2024-03-08 6:00 774 miles

Car unlocks/locks properly. A good sign.

2024-03-08 8:15 774 miles

12v battery is dead again. This time, the car was only idle for less than 24 hours. This time I use my own emergency battery charger to boot it up again, as I already have an appointment that I need to get to by 9:00 at the same Toyota dealer for a key. No time for Toyota Roadside Assistance as I can’t have my whole day taken up by car appointments.

After I get the car started, I get to my appointment and I let them know that I’m extremely frustrated. I have a different service advisor who listens to my problem and seems to understand that I know what might be wrong with the car, and that I’m not just killing my car and taking it to the dealer to inconvenience them.

In the meantime I call Toyota’s Brand Engagement line, because I want to get ahead of the problem, since the dealership isn’t being responsive enough, and is trying to pass the problem off on user error.

I leave the car overnight and ask them to diagnose the car again.

2024-03-09 10:52 785 miles

I get a text from a third service advisor asking me to drop the car off. The car has been at the dealership for over 24 hours now and they clearly haven’t scheduled further service, and they don’t know where it is. The car is parked at the dealer lot, where I left it with the service center. Concerning, but I let them know that they have it.

2024-03-09 14:35 785 miles

I get a text with the same diagnosis as before: everything green, battery is fine. Nothing to service. They report checking the battery and looking for abnormal electrical draw, but nothing further.

I pick up the car an hour later and talk to a service advisor and a technician on the shop floor, and I don’t get a satisfactory answer to the question: “what is causing the car’s 12v battery to die in a day or two, and what is going to prevent me having to come back over and over again to have this issue left unaddressed?” Their stance is that they can only do so much under warranty, but my response is that it’s a new car from their dealership, and no one is accountable for the car being unreliable and potentially undriveable on a daily basis.

I take the car home because I don’t believe they are doing any further substantial diagnostic work beyond “check if it turns on” if I leave it with them for another couple of days. I feel like my time is being wasted. I am nearly certain that will be back in a few days anyway, since the 12v battery is likely to die in my driveway again.

2024-03-10 13:22 801 miles

After a 14 mile drive home from the dealership, and then charging the traction battery from 43% to 100% overnight, I decide to test the 12v battery again at the local auto parts store.

The 12v tests at 12.24v (nominally unhealthy and I assume about to get knocked out again if left overnight).

 

Yeah that’s not good. Maybe get a Solar BA9 or similar, one of the new Gen of 12 volt battery testers, see what it says.

 

Ask the dealership to do a Battery Load Test on your battery.
Ask for a printout of the test results.
If a sulfated battery is indicated as a test result, ask them to replace the battery under warranty.

 

I have done this twice and I’ve seen a “good” test result. It’s probably not the battery. Something else seems to be keeping the car awake and killing the battery.

It will be my battery as well eventually if they don’t find the root cause, since this battery can’t handle the abuse from the car’s electronic system. At least that is my working theory.

Some people are having batteries that test bad, but who knows if that is from repeated draining rather than a manufacturing defect, since these batteries might even be fine from the factory.

 

I say again

"Ask the dealership to do a Battery [Load] Test on your battery.
Ask for a printout of the test results.
If a sulfated battery is indicated as a test resullt, ask them to replace the battery under warranty."

Get a Toyota Dealership implemented battery load test with a written report.
Post the report here.
Do not be put off by the dealership to have the test done others. Get the written report from the test. DO not accept a verbal description of the report

 

Here are summaries from tests that I have gotten. I believe that they did the tests and that these are the honest results, but the car is still going to die in my driveway regardless. It has twice in the past week, and I expect it to happen again Monday or Tuesday.

One independent test also rated it as good, and a more recent one rated it as bad. It’s headed for the recycling bin if they don’t do anything about it, diagnostics aside.

I am guessing that all failed or eventually recalled parts get tested as acceptable at some point in service before they fail. In this case, I think it’s a systemic issue, not the battery itself, but it’s going to needlessly kill batteries either way.

 

I see your test results in the image attached. I will try and post a pdf file of a
"Battery and Electrical System Analysis Advanced Battery Test
Advanced Battery Test"
Might be the same test you posted results from, but different rresults. This came froman older post to this forum, not Gen5 post. I cannot locate it now.

 

This is similar to the second test that they did. I imagine in a week or two I will see “Sulfation/Degradation” on that report, unfortunately. But right now it reads “good”.

I will get the battery replaced under warranty when it tests bad, at immense personal cost to my time, and ability to drive a new car. I’d rather the car get lemon status at this point if I have to go through another week of this. It’s enormously inconvenient to know that my car is going to die in a parking lot no matter what I do.

My next step is to escalate further with Toyota corporate and this useless local dealership. If it’s going to cost me my time, they’ll have to share the burden since their warranty is not holding up on their end of the contract.

 

Leave the car in your driveway. When it inevitably dies again, have them *tow* it on the flatbed with Toyota roadside. Have them figure it out from there. Maybe it'll be different if you don't boost and drive it in.

 

Update:

2024-02-11 2:15 806 miles

The Prius Prime is dead again after only 5 hours of not using it and I caught the failure to start at 2:20 AM on video this time for the benefit of any technicians who want to watch the systems of the car fail one by one as the 12v loses its last bit of power alongside a cascade of error messages having to do with the parking brake and Park mode.

I couldn’t even get enough power to open the rear hatch which would have been nice to be able to open, but there was enough power to attempt getting into READY state. The first sign of failure was that the braking system could not get enough power, and caused an anti-lock braking type of shudder as it failed to develop pressure during the boot sequence. I believe this must be one of the higher power requirements of the car when starting up. After that I saw a lot of flashing interior and exterior lights during my process of trying to get the car started.

The car was unplugged and the traction battery was charged to 80%+ from earlier in the day after getting an 100% charge less than 24 hours ago.

 

TIme for a new battery. I beginning to wonder if there is a bad manufacturing lot of batteries out there causing this issue.

 

Could be. I told them they can replace the battery if they want to, but only if it fixes the underlying issue.

I’m concerned that if the battery is fine, but the draw is 5v at 2 AM Monday after testing good on Saturday afternoon, driven 20+ miles and traction battery charged overnight Saturday for 5 hours, then the power draw while idle in the garage is the actual symptom and the battery is being killed as a side-effect. That is my theory and a lead technician here initially agrees.

I’ll keep posting if I find anything solid since this is one of the worst cases that can’t be attributed to a bad battery alone. Hopefully this is helpful to someone facing similar concerns. I don’t think I would have had an understanding of this issue up until this point without reading this forum.

 

I want to call this out as the right advice at the right time. I saved 15 pointless miles of wear on my car and showed them how severe the issue was. They took it seriously.

I did have to boost it since I couldn’t even get it out of my Prius-sized garage safely, but that was inevitable since it didn’t even hold a charge long enough to make the car accessible for a tow truck driver. I was going to park it out front to make it towable, and then it died outright.

What a Prius with a dying 12v looks like: https://we.tl/t-ROl0h0COvy

In that 10 seconds, I am pressing the brake the entire time, and start/stop button only twice. I did some variation on that for 15 minutes until everything on the car failed except for the Bluetooth lock/unlock and Toyota app notifications. The doors had no power to lock, so it was irrelevant, but the car could still send data to my phone while everything else on the car was almost completely dead.

 

The video link doesn't work. Just says the file can't be previewed. Did have to agree to the cookies first though which I promptly deleted. You may have said this already but what aftermarket devices have you installed?

 

You know, perhaps Toyota should implement a "zero draw/ cold off" mode controlled by the physical key. Then you could park the car in airport parking for two or 3 weeks and return to a fully charged vehicle. That could be done with firmware modification only (thus minimal cost) and solve the battery drain issues of the infrequent driver/ retiree/ airline traveler.

Regards,

KD5TXO

 

Don't know about the video, but I think you need to select "I agree" to terms and conditions on the site and then the link to download shows up. There's not much to see since it's only a 10 second clip.

Absolutely no accessories. None from the dealership either (they confirmed this multiple times). I was going to walk from the sale if they added anything.

I do have a Toyota Integrated Dashcam that is sitting in a box ready to install, but this issue prevented me from installing it.

 

$.02 on battery testing..

Battery should be removed for testing. Leaving the battery in and just opening the hatch will leave the inverter on which will skew results. Too many are too lazy to actually do this, the workaround is leaving the hatch open for 30+ minutes so the car can shut down the modules and quit charging the 12V battery from inverter.

Sure fun how some people at shops test these.

 

2024-03-14 14:21 829 miles

Car has been in the shop from 2024-03-11 to 2024-03-14. It has been driven about 23 miles while in the shop (not by me). 12v battery has been replaced with a new battery.

Service department reported that the previous battery had failed. They report no parasitic drain at 0.014A idle draw. New battery tested at 12.2v overnight and is charging properly.

Traction battery has been charged by the service department to 84% (5.356 kWh added).

Loaner handed in.

2024-03-14 15:47 842 miles

13 mile snowy drive home from the dealership, EV-only at 4.5 mi/kWh nominal efficiency. Car locked and garaged. Nothing to report.

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I’m happy that at least something has been addressed. I don’t have a lot of confidence that this is the fix, but we’ll see. I am documenting everything trip by trip with photos and notes to make sure that this gets caught immediately if it fails again.