Parasitic battery drain?

Yep, I would consider this for long-term maintenance and would recommend it to anyone with an initial diagnosis need.

At this later stage I want them to handle it completely, since their “nominal good” tests are valid enough for me to know the problem is too complex for a home evaluation to convince them to take action. If I go there and tell them I found the battery or draw tested bad at home, they wouldn’t take me seriously anyway and would need to verify it. I think it would have been the same story, since their diagnostics are “better” than an independent test from their perspective. I do want their valid test in my driveway since it fails there the most, but that’s not a method they are likely to find acceptable or worth doing.

 

Another thread “what is this?” was about the battery sensor located on the negative terminal of the battery. On mine I am wondering if it’s ok and how the factory manual says to test it. I believe it is a battery monitor that regulates charging the 12 volt. It is supposed to be somewhat delicate. I see a black and a white wire on the connector. I assume that’s + and-. I guess I will dig into it more. My car is ok, not dead, but I charge the 12 v manually quite often. I saw a news article just today about ev owners getting dead 12 volts and being perplexed. It isn’t just the Gen 5, or Toyota. My Gen 2 was not keeping the 12 volt well either.

 

I have some traction battery charging data to share.

Car has been charged 20 times in the past ~30 days and 150-800 miles, all at home, all on the standard 120v L1 charger.

2/20 sessions were below 1 hour.
14/20 sessions were below 5 hours or 3 kWh.
6/20 sessions were above 5 hours or 3 kWh.
2/20 sessions were above 7 hours or 4.5 kWh.
0/20 sessions were above 8 hours.

9/20 sessions charged to 95% or more, and all involved driving within a day and never leaving it sitting on the charger. So it’s being charged roughly every 0-3 days, which means it’s being driven about that often.

I didn’t have time to put it into a spreadsheet to graph it or share the raw data and I don’t think I need/want to. But this gives a general sense of how I’m not leaving it on a charger. For the first month, I have been wanting to run the gas engine on highways (trips to the airport, longer local/regional drives) to understand how the car performs in different conditions, and get rid of the existing tank of gas in case it had been in the car for too long. I haven’t run it in charge mode except to test how it works.

I looked at my Drive Pulse data and while I can’t begin to share that here for privacy reasons, it’s on the low end of “Excellent” with a lot of 2-5 mile trips and frequent 5+ mile trips (nothing over 80 miles round trip).

 

I would still clip on a battery monitor and watch what’s happening myself in real time rather than guessing and spending time at the dealer. But I would unclip it going to a dealer because when they see it they will say that is the problem. Like the battery dead in 5 hrs, what was the beginning state of charge? Or how is the car charging the battery during driving? On my G4 I keep the 12 volt up pretty well because I know what is going on.

 

Testing the battery in use is a good idea, but I’ve already handed over the car to the dealership indefinitely (probably a few days, but who knows). Since the problem was so severe, giving my testing data to a dealer probably wouldn’t convince them of anything. The technicians are mostly interested in my usage and subjective experiences with the car, and anything else I assume they can mostly get from the car’s own data logs.

As far as the beginning state of 12v battery charge, it was likely poor, but let’s take a look at the timeline (normalized for DST, 24h time for my sanity):

• 2024-03-09 Saturday 15:00 – completely charged at the dealer after testing good. The car has been at the dealer lot since Friday 8:15.
  
• Saturday 16:00 – driven 14 miles home.
• Saturday/Sunday overnight 00:05 to 5:50 – left on the charger overnight to charge the traction battery 3.6 kWh.
  
• Sunday 13:00 – driven 2 miles to the local auto parts store.
• Sunday 13:22 – tested it at 12.24v at a local auto parts store – I am skeptical of the accuracy of this reading, but it’s not healthy.
• Sunday 13:28 to 13:45 – driven the long way home on a hillside drive to see how the car is doing (looking for warning messages, hopefully getting some charge into the battery). Everything is great. Parked in the garage and I don’t plan to use it for another 24 hours for an appointment that I have. I have my doubts that it will be driveable for my appointment, so I start planning ahead for failure, and a third visit to the dealership.
• Sunday 19:39 – car unlocked, tested that it will boot into READY without errors, locked, check all lights are off.
• Sunday 22:00ish – test remote READY start, runs for 20 minutes successfully – I do this to see if I will be possibly be able to pull the car out of the driveway for a tow in the morning in case it dies. In retrospect, I should have taken this opportunity to park it outside.
• Monday 2:09 – car has enough power to unlock the doors but not to do anything else.
• Monday 2:10 – car won’t start and 12v dies.
• Monday 4:24 – Toyota Roadside (AAA contracted) support measures the 12v battery at 5.8v and the battery is boosted to get the car into the road to be towed. I would have preferred to leave the car dead for diagnostic reasons, but it’s a very small garage and it would have been almost impossible to get it out of the garage without damaging something.

That series of events suggests to me an extreme draw while idle, but there may be other plausible explanations. The supporting behavior is two dead batteries on 2024-03-05 and 2024-03-08 after “normal” use of the car.

Keep in mind that the vast majority of driving going on during this week of failures is to and from the dealership (735 miles to 806 miles), and that I am only in possession of the car for just over 2 full days in a 7-day period. I’ve spent almost as much time in Lyfts and loaners as I have in my own car this past week. I’m all for testing the car, but there are very few hours of the week that I’ve even had it in my hands to test, because it will stop working if I leave it parked for more than a few hours.

 

It's probably not going to happen to your car.

I am sharing this so anyone can chime in and say "me too", and if they do, they will have a better idea about how to handle it under warranty, since most dealers will fail to initially diagnose it. And if I'm the one of the only ones, that is excellent, since it won't happen again often.

Also, isn't the battery in the 2023-2024 Gen 5 a flooded lead acid battery not an AGM? I'm not clear on this as people sometimes call it an AGM battery but it doesn't appear to be one.

 

I think there’s a positive value in this. Additionally, this thread also features good discussion of common causes to a drained 12V battery in our vehicles that can be relatively easy to rule out. Just because multiple people are experiencing drained 12V batteries doesn’t mean the cause is the same for every individual.

Has the dealer service department reached out with any new info?

 

I agree – the more that I have read on the issue, the more I think there are a few different problem areas, and I might have one or two of them.

The current status is the same as yesterday all day: the service advisor says via text this morning that they are still actively working on it. I get app notifications regularly suggesting that the car is being checked on multiple times per day - unlocked, windows open, and so on. I have received follow-up questions from the advisor and lead technician about the last day I had driving the car, and whether the key has been ever been left in the car ("never"). I am responding politely and thoroughly. I like that they are looking into the issue and I want them to work on it for as long as it takes to get to a conclusion.

 

Where it is, is the deciding factor: it’s back in the hatch area IIRC, and if so it’s AGM.

 

As far as we can see, it's not. Some recent discussion over here - it seems to be a variant of the battery fitted to the G4, a bit smaller and with the pressure-release valves removed, so relying on the vent hose. In a Facebook post at the time of the G4 release, the battery manufacturer said "The 345LN1-MF is a calcium base superior MF battery enabled by the patented double lid structure. It employs a central degassing structure and therefore can be used in vehicles in which battery is installed in the cabin or in the engine compartment. It is not a AGM battery."

Toyota's New Car Features for the G5 says:

"An EN (European Norm: European Standards)-compliant and open type battery is used for the auxiliary battery, and it is installed under the luggage compartment. A battery hose is provided to effectively direct gas generated by battery electrolysis out of the vehicle.

Auxiliary Battery Type: LN1
Rated Voltage: 12 V
20 Hour Rate Capacity: 45 Ah
Cold Cranking Ampere (CCA): 285 A
Ventilation Type: All Cells Combined
Indicator: Equipped
"

What did you find online?

 

Ah ok, I stand corrected.

 

Interesting back-and-forth!

One of the things I have been finding is that there is a surprising amount of confusion and minor bits of misinformation about the Prius in general and especially the newer ones. So much is similar to the previous gens, but there is enough new that it’s often hard to get a straight answer to some questions. Even a year into this car being on the market and it having sold in the tens of thousands, I’ve had to scour forums to find accurate parts numbers and basic technical information about these cars. Sometimes the community has had better answers than dealer sources.

Three things I ran up against:

• Parts desk at a different dealer was helpful with technical questions but couldn’t give straight answers on wheels and was discouraging any questions I had about making a second set of wheels for winter work, which made me decide to never ask them for advice again and not buy parts there unless I absolutely have to.
• Tow service guy who was also extremely helpful and knew Priuses from towing them, when I said “the Prius Prime doesn’t have an alternator so it makes the diagnostic path different from a conventional car with a failed battery”, he replied strongly “yes it does”. Hm. I didn’t know how to respond without sourcing my claim so I dropped it.
• Online parts departments from dealers are completely incapable of looking up newer Priuses by VIN (as of late February 2024), and have almost no parts that are listed in their verified fits for 2023-2024 models, yet some of the parts must fit and are just not updated.

This is why I have been reading these forums, since folks here are trying to answer some of these sorts of questions and solve problems.

 

I saw 98-100% state of charge as I got back home today. The trip was 12 miles total, town driving. Started at about 77%. Maybe it was just a dream. But I am not just wondering what it is.

 

12 volt battery failing to start the car | Page 9 | PriusChat

On the path to resolution? The car received a replacement 12v battery today.

If it doesn’t fail again this year, those who guessed “bad battery” were likely correct.

If it does fail again with a new battery, is it an extraordinarily rare lemon with some defect that the diagnostics can’t catch?

 

Glad to hear you got a new 12V battery under warranty!

I do wonder how they determined that the battery was bad and what different assessments of the battery they did this time around that they did not so in your previous visits to that dealer service department?

 

I wondered exactly the same thing, but I know I can’t get a straight answer about this. For all I know, Toyota or the dealer service manager told the shop floor to “do what they can” which under warranty is to replace the battery and hope for the best.

If the car legitimately dies three times in a week under very little stress, but also legitimately cannot diagnostically test bad after sitting at the dealer for 7 days, they are at an impasse. That is why I’m a bit worried that this is a “wait and see” cheap fix.

Pressing them for a straight answer may not get me closer to resolving the issue. But I will be asking them again and again if the car fails. If it goes back a fourth or a fifth time, it’s time to start bugging Toyota.

Car started up this morning, no surprise.

 

This mirrors my experience, except they are being even more dismissive to you.

The interior or exterior lights can't drain the car that quickly, and auto headlights turn off within a minute of the car being turned off. Not only is this not "working as designed" – it will eventually kill that 12v battery.

Talk to Toyota Brand (number is in your manual) about it and keep up the pressure?