Prime 2023 12V battery integrity on EV

From Toyota: "Your profile preferences and settings can be modified in different areas depending on what you’d like to change. Some preferences, such as radio favorites, display day/night mode, seat settings, display language, etc. can be changed and stored within your profile as you adjust them in the vehicle. Other personalized profile settings such as your profile name and profile image can be changed from within the Toyota app." - so it at least restored my radio favorites and other preferences when it loaded my profile. Whether it restored some of my other preferences (for all the safety options) I have to check.

 

Settings are stalled all over the place in various ECUs. Some will be non-volatile and survive battery disconnection, some won't.

The intro to the multimedia section, for example says:

Could also be the case that the "My settings" stuff is saved somewhere that survives a 12V disconnect better.

 

From what you & @nagrath have said, I oversimplified when I said (message #36) that "Toyota does not use flash (non-volatile) memory to store the owner's configuration choices." It seems to be a hodgepodge, consistent with the observation that the designers of the instrument-cluster UI seem never to have spoken with the designers of the multimedia-screen UI.

 

Ha! I absolutely agree! And neither of them seem to have ever driven the car for any length of time!

 

This is getting tangential, so I started a new thread.

 

I have been exploring the properties of the 12V battery. Here is an interim report.

I have the Motomaster meter that I mentioned in post #39 above, but I am no longer using it. It works only when the car is in Accessory mode, and its readings then are unstable. (I don't know why the readings are unstable. It could be a defect in the meter, but it could be that Accessory mode is a fairly active time for the 12V battery, so it is running various checks, some of which draw more power than others.)

In any event, I want to see the 12V battery's rate of discharge

• during charging of the traction battery,
• after the traction battery is fully charged, but while it is still connected to its charger, and
• while the car is parked and disconnected from the charger.

The best way to do this would be to have an ammeter connected between the 12V battery and everything else. The ammeter would have to have a wide range, from the slow discharge when the car is sitting idle (milliamps, I expect) to the charging current when the car is being driven (amps, I expect). I don't have an ammeter with the required simultaneous range and precision. Also, I am not eager to break the 12V battery's connection to the car, even transiently.

As a second-best solution, I have connected a digital voltmeter directly across the battery, with output visible from outside the car. It reads continuously, without having to bring the car up to Accessory mode. It draws about 10 mA itself, so it will overestimate the 12V battery's rate of discharge.

With the traction battery fully charged and the car disconnected from the charger, the 12V battery's voltage went from 12.6V to 12.2V over the course of 50 hours. Modeling the drain as a simple exponential, I compute a half-life of 1065 hours, and the model predicts that the battery would take another 25 hours to get down to 12V, and 125 hours after that to get down to 11V.

The ambient temperature during this experiment ranged from 7°C to -10°C. I don't know what temperature is low enough to cause the battery heater to turn itself on. If the traction battery had been activated to service the battery heater, it might have incidentally trickle-charged the 12V battery, accounting for the 12V battery's slow apparent discharge rate. To see if this might be true, I briefly (a few seconds) turned the car on, to see if the traction battery was still showing 100% charge. It was.

The drain on the 12V battery from just those few seconds of electronic activity was non-trivial. Immediately after the car was shut down again, the 12V-battery voltage was 11.7V.

More data to come.

 

The battery heater only operates when plugged in. And when battery temperature is in a range of around -10°C to 0°C, or maybe a bit wider.

 

That describes the same behavior I see in ACC mode using the Car Scanner app.
Try putting the Prius in READY mode after you are finished taking readings in ACC mode and time how long it takes to bring the 12 volt back to your cars normal OFF floating voltage range.

Again, 11.7V is within the normal range I see in ACC mode, but that would be a slightly low reading if I had switched into READY Mode for a ( few ? ) minutes before shutting down.

 

I will do that experiment, but in the meantime, I have a new finding. A few minutes after going OFF (12.2V) to READY to OFF (11.7V) as described in post #46, the car remained OFF, and the voltmeter showed 12.2V again

. The 12V battery behaves as if it needs a few minutes to redistribute charge internally, so while a brief small power draw might cause a brief decline in the output voltage, the actual charge lost might be so small that the output voltage is not changed (well, changed less than 0.1V) after the battery has had a chance to re-equilibrate,

 

I overlooked the fact (pages 108-109 of the Owner's Manual) that the heater is charging-cable dependent. Where did you find the specs of the temperature bracket?.

 

If I'm reading your description the way you're actually seeing those results, the name of that is voltage rebound. Which normally happens any time the load is removed form a healthy battery. A load typically reduce voltage in a battery as it's dis-charging and if monitoring the voltage during discharge under load, removing the load allows the voltage to rise and float at it's current state of charge.
It can even be seen with the traction pack when monitoring it using DrPrius, but it takes a close observation to identify it.

 

I've never found actual specs, but read others' findings and did some research of my own on the lower bound recently:
Battery heater not working? | PriusChat

 

here are some specs on the Gen 4 traction pack heaters from Weber Auto
youtu.be/yGMcQ6JWlBs?t=411

If there's enough interest we may get a similar video about the Gen 5 Prime eventually.

 

I had expected to report some solid data by now, but the properties and dynamic environment of the 12V battery are more complex than I had thought. Here is what I have so far:

• When the car is in READY mode, the voltmeter across the 12V battery shows about 14.6V (from the built-in charger).
• When the car is powered off and the 12V battery is fully charged, the voltmeter shows 12.7V.
• When the car is plugged in but not charging, and the temperature is above freezing, the 12V battery's voltage decays so slowly that its decay rate is difficult to estimate, and it may be dominated by the 10mA draw of the voltmeter itself (I could collect data with the voltmeter connected only intermittently, but the pertinent time constants are already so long that it would take weeks or months of parked observation to get stable estimates). For what it's worth, the half-life of the voltage seems to be about 2000 hours, so after about 50 hours the voltage is down to 12.4V or so. These data were obtained at ambient temperatures of 0-5°C.
  
• At lower temperatures, the 12V battery sometimes continues to discharge, but sometimes charges, with the observed voltage sometimes transiently as high as 14.3V.
  
• I don't know how to tell when the battery heater is running, but all the above data are consistent with the 12V battery being charged when either (a) the car is in READY mode or (b) the car is plugged in and the battery heater is running.
• I haven't had an opportunity to follow the 12V battery voltage while the traction battery is getting relatively deep recharging at temperatures well above freezing.

 

I recently watched a video where John Kelly (Weber State) went through the battery on a Gen 4 Prius Prime. One of the things he pointed out was that when you charge the EV battery, the charger also charges the 12V accessory battery. There are some really good reasons why it does this (one of the reasons is to guarantee the cooling fans run, which use 12 volts from the accessory battery). I suspect the Gen 5 (which has a much larger EV range so it's going to have some improvements) uses something similar but builds on this.

 

@Fenichel It's been well below freezing here for the last 2 weeks (lowest was 8 F / -22 C) and I've been keeping the Prime plugged in for a couple of days between drives. Once by chance I noticed while the Prime was plugged in and had been sitting for a few days that both the charge port light and the 3 LEDs on the passenger side of the dash were lite which was the first time I'd ever seen that, besides when I manually run the 10 minute pre-conditioning.
@Danno5060 I think many of us that have seen that video at least once, are hoping that Prof. Kelly will eventually publish a similar video for the Gen 5 Prius and / or Primes Traction Pack specs and or improvements made form the Gen 4

 

Add my name to the list of owners with a defective 12V battery. We were away for 9 days with the car in the garage. Returned home to find the 12V completely dead. Got a battery boost and was able to start it and get it to our local Toyota Dealer. They've told me that the battery is defective and is being replaced. We purchased the car in September 23 and have never used the ACC mode. Its been driven regularly probably more often in EV mode. 4400km on the car. Not impressed.

 

I noticed the USB port lights on when I was in the garage once too. They turned off at some point since I checked again 5 mins later and they were off. I thought I had left something in but it was only the usb lights and nothing was plugged into them.

Strange. But they're teeny tiny led so there's no way that light alone could kill a 12v quickly

 

I'm 99% sure the USB lights are in the same circuit as the footwell lights(for the trims that have them). That means they shut off either when you lock the doors or when the timer goes off(something like 90sec to a couple minutes).

 

Any idea if the replacement is supposed to be an "improved" version or just the same but new?
Reading through all these Gen5 12V complaints here and on Reddit makes me wonder if there are any better alternatives than what Toyota provides under warranty.