12V battery going dead

i congratulate you on your patience. i'd be on the horn with toyota, and a lemon lawyer before modifying my brand new car.

 

I think you do need a battery monitor to see better what’s going on, and a days long record in a graph. Im still puzzled about what is going on with my 20 Prime. It always charges the 12v when in park in the driveway. Once I just left the car on awhile to charge the 12 v. Nothing is consistent day to day while driving. Sometimes it charges very well, other times charging is off. I will figure it out.

 

Again, that is a moot issue. The problem you are having is specific only to you and has nothing to do with the design.

Do you realize that the 12-V battery has a 0.6 kWh capacity? The HEV reserve on the traction battery is only 0.9 kWh. Even the traction battery cannot keep up with a 12-V battery that drains every two hours.

You need to have the dealer repair your car under warranty or, if it cannot be repaired, return it to Toyota. Then report the outcome here. You are wasting your time and energy by trying to bandaid a serious defect in a brand-new car, which no one else has. And again, why?? The car is under warranty. It won't be under warranty for too long. What you are trying to achieve makes absolutely no sense whatsoever.

 

Nope, you don't understand how the hybrid system works. When the 12-V battery is dead, the car cannot even start the computer to do the tasks you want. The only remedy is to charge it externally. It cannot be charged internally with none of the car systems able to start up. This is not a 1980s car.

Again, you are wasting your time. There is something wrong with your car. It could be as simple as a bad 12-V battery or something more complicated as a short circuit or a faulty component. Have it fixed under warranty.

 

Why is this so difficult to understand? The cars' systems, including its computer, won't start with the 12-V battery dead. The car cannot communicate with the traction battery, DC converter, etc. without power from the 12-V battery to recharge the 12-V battery from the traction battery.

If it helps, think of it as a catch-22 situation.

 

No, I understand your simple point perfectly, but you are not understanding me at all. I am not talking about the traction battery going dead or not having enough power. Let's assume that the traction battery is fully charged for argument's sake.

I stated something else that you haven't understood, and you think that I am talking about the traction battery going dead, which I am not.

My point was that the traction battery is inaccessible with a dead 12-V battery, as the car's computer and communication systems are inoperational with a dead 12-V battery. So, it is impossible for the car to charge the 12-V battery from even a fully charged traction battery if the 12-V battery is dead.

Read my previous post a few times. If you still don't understand it, perhaps others can explain it to you.

 

Basically, you are suggesting to use a second 12-V battery to fire the computer and communications up in case the primary 12-V battery dies. Do you have any idea how much current the 12-V system draws? It is around 50 A or perhaps more. “A small rechargeable cell” as you suggested above wouldn't work. It is not like a backup battery for an alarm clock. If it were, the car would still fire up even with very little charge left in the 12-V battery, and there would be no need for the small rechargeable battery you suggested to begin with. While people might think that you don't need a very large current to start an EV as you do to crank the starter for an internal-combustion engine, this is not true—you still need a very large starting current before the DC converter can take over. I said about 50 A, but it could be even higher. This is why the CCA rating for the Prius 12-V battery is important even though the car has no starter.

It is simply not practical to have two 12-V batteries: added weight, added cost, reduced space, reduced fuel economy, etc.—not to mention how ridiculous and unprecedented it would be to have two 12-V batteries. And a small rechargeable battery wouldn't be able to provide 50 A of or perhaps more current needed to start the car electronics.

Last but not least, do you think that the Toyota engineers are not capable of thinking these things?

 

Just like you were right on the AGM vs. flooded-cell topic with your 100 false posts and everyone else in that thread was being argumentative, right?

You need to start the entire 12-V system to be able to communicate with the DC–DC converter and traction battery. That takes an initial current of about 50 A. However, you don't get it. Just like you didn't get anything we explained to you in the AGM thread. And, even worse, you have never showed any remorse after you found out that you were wrong all along.

Most of the current does not come from the DC–DC converter. All the current comes from the DC–DC converter. Except, the current comes from the DC–DC converter only after the system is started. And the system won't start with a dead 12-V battery. And if the system starts, then the 12-V battery is not dead to begin with. And you need about 50 A to start the system.

You still didn't answer the question I asked you: Do you think that the Toyota engineers are not capable of thinking these things? Alternatively stating the question, do you think that you know better than the Toyota engineers? If so, did you do any formal study in science and technology beyond high school?

 

Thought I read Toyota has a software fix now.

However you can buy a 12v battery that has a reserve built in. If the primary capacity is discharged it goes into sleep mode and a wireless remote engages the built in reserve on demand. Primarily used in expensive supercars with long periods between use.


Pricey but…

Group-24 Lithium Car Battery – Antigravity Batteries

 

LoL; I think I'll stick to a jump pack. or take my chances with the 8-10 batteries I could buy for that price.

 

There’s been other reports here.

Okay. Who HASN'T had a 12V battery issue with their 2023-24 Prime? | PriusChat

again, if a few owners could do a careful check of at-rest amperage readings, it’d help.

 

Old knowledge I guess. I don’t know why car and driver mentions alternators but doesn’t matter. For the hybrid model in 2017 Hyundai did do something about the 12 volt issues. Carrying a battery pack would do the same but more trouble. Or install a battery monitor.


https://www.caranddriver.com/news/a15341302/how-the-hyundai-ioniq-ditched-its-traditional-12v-lead-acid-starter-battery/#