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

Six month update: no further issues at 4,810 miles, since March 14 12v warranty replacement.

A dealer replacement of the faulty battery completely fixed my problem.

 

Another benefit to using a battery monitor is to observe how battery chargers actually work. I have a few different chargers, none are the same.

Actually I am a bit surprised you come up with these things. I erased everything else I wrote.

 

Not sure what you meant by that, but what I said was that the 88% SOC shown in your previous post was incorrect because it should be 99% at 12.63 V for an open-circuit and rested flooded-cell. It could be that the monitor was calibrated for an AGM battery or is making some wrong assumptions. I also said that your monitor has no way of knowing whether the battery is being charged or not [because it is not measuring the current]. So, I am pretty sure your conclusion that the battery only (or mostly) charges when you put the car in park is incorrect, and what you are seeing is an artifact of the monitor caused by small changes in the DC–DC converter voltage when you shift from drive to park.

 

So, what is the troubleshooting procedure?

 

Unfortunately Toyota TIS terms of service do not allow sharing of data downloaded.

Readers Digest version summary is confirm battery health. Check for DTC in history. Perform dark current check (parasitic drain). If dark current less than 120 milliamperes, system ok. If above follow procedure to isolate system causing high current.

The TSB which I believe is a potential root cause of aux battery depletion is available on this forum. I suggested to the SA that the TSB be followed for my car. Gave him a copy. Doubt it got passed on to the tech. However, I did note on the final RO the copy of cover sheet for TSB was stapled to RO.

in the back of my mind was the concern of them doing the firmware update. Not sure of this dealer’s technical savvy in this area. For me right now, I have a battery monitor installed which is quite insightful. Plus I disconnect the charge cable asap. To date, no issues since the lone occurrence on 14 August

Cheers

 

Get one of these things and try it to see if it is the same. Return it if you think it is fake news. It definitely shows charging or not imo. The battery is always connected. The other battery has unusually high voltage. I charged it some days ago with a little charger and it went to this higher voltage.

 

0.120 A is a lot of parasitic drain if it happens continuously. It would drain the battery in a couple of weeks if not less.

 

The TSB might be too difficult for them to follow their procedures on. Often they refer to a concrete diagnostic code. This one just says:

"Confirm the condition exists. Does the vehicle exhibit a condition where the 12V auxiliary battery charge may deplete due to the plug-in charge control ECU not entering sleep mode when the PHEV charging cable has an extended connection without charging?"​

So just repeating the description from the introduction.

There's no clear test the dealer can perform for that, they're just going to have to take the owner's word for it.

And I can imagine a lot of dealers have rules about not just doing TSBs on-demand to make sure the warranty claim is valid and they get paid.

I don't see much verbiage on these US TSBs, but European ones say stuff like:

(That's not for this TSB, that's for a head unit update - an equivalent for this charge ECU doesn't seem to have been issued in Europe yet).

Meaning this one gets stuck in a catch-22 - they're not comfortable doing it because of something the customer says, and the TSB doesn't explicitly say customer complaint is enough, but that's the only way to satisfy the requirement on the TSB.

Need to find a better dealer...

Or do it yourself? Can you download calibration files with the sensibly-priced Techstream subscription in the US?

 

Thinking after overnight, the 88% you think is 100% soc, if I put a charger on it will start charging, watching it climb 89 90… until the charger turns off later, then it says 100%. So the 88% is not 100%. I know about the charts and have before the internet.
Or, can sit in my driveway in Park, and watch the soc climb 88 89 90 until 100%. If I drive one minute, charging stops. Put in park, starts charging again, 88….

 

I have a battery monitor installed and a voltage display adapter that plugs into the 12 volt outlet that reads battery system voltage when car in READY mode.. I have confirmed accuracy of both to my VOM hooked up at battery terminals. Its been quite interesting to see how the aux 12 volt battery charging system works. This morning, the battery voltage was 12.4 volts per the battery monitor. On car start and READY annunciation, the voltage was 14.1 volts. 3 minutes into the drive in HYBRID mode, the voltage drops to 12.8 and remains there the remainder of the 16 minute trip. I believe this is done for improved economy. Ditto experience for the return trip in EV mode. 4 hours later in the garage, the current battery voltage is 12.36. My experience has been that the battery voltage I see in the morning or not having used the car the day before is 12.3 to 12.4 volts.

My experience has been that the charging voltage will default to 12.8 after a period of driving. Basically, this is a maintainer or trickle charge. Per Toyota information on TIS, this is how the system is designed to function:

BATTERY SENSOR

(a) The battery state sensor assembly is installed to the negative (-) battery terminal side of the auxiliary battery. The battery state sensor assembly calculates the current, voltage, temperature, SOC (battery charging rate) and SOH (battery deterioration level), and sends signals to the hybrid vehicle control ECU via the LIN communication (data bus).

(b) To detect the current of the auxiliary battery, a shunt resistor installed inside the battery state sensor assembly is used to convert the voltage that is generated in the shunt resistor due to the battery charge and discharge current and calculate the current.

(c) The auxiliary battery temperature is calculated from the resistance value of the thermistor built into the battery state sensor assembly.

SYSTEM CONTROL

(a) Basic Control

(1) Controls the output voltage of the hybrid vehicle converter assembly (DC-DC converter) in accordance with changes in the target SOC to change the SOC of the auxiliary battery to reduce the power consumption.

(b) Constant Voltage Control

(1) In the following situations, basic control is temporarily suspended and constant voltage control is performed.

1. A certain period of time has elapsed since the power switch is turned on (READY).

a. In order to compensate for electricity consumed due to parasitic current when the power switch is off, constant voltage control is performed for a certain period of time after the power switch is turned on (READY).

2. Stable operation of certain electrical components is required

a. The state of certain electrical components is monitored, basic control is temporarily canceled and constant voltage control is performed when the system determines that operation of the electrical components may become unstable.

3. Stable use the auxiliary battery

a. Constant voltage control is performed and the auxiliary battery is fully charged every 20 driving hours to minimize deterioration of the electrode plates due to sulfation by repeating charge/discharge of the auxiliary battery.

b. Constant voltage control is performed when the SOC of the auxiliary battery is low or the temperature of the auxiliary battery is high/low to minimize deterioration of the auxiliary battery.

(a) Power Consumption Reduction

1. (1) Carrying outs from high voltage battery decrease by reducing the work load of the hybrid vehicle converter assembly (DC-DC converter), and the mileage improves.
   
   
2. (2) The vehicle is comprised of a large number of electrical components (ECU, actuator, motor or light). The hybrid vehicle converter assembly (DC-DC converter) depresses the voltage of the high voltage battery and supplies electricity for them.
   
   
3. (3) Because the electricity is the product of the voltage and current, the power consumption is reduced so as to lower the output voltage.

My understanding is the car comes with a lead acid calcium battery. Personally, I am not knowledgeable on this type battery. That said, I'm not sure how well an AGM battery would function with Toyota's charging system design.

Hope this helps understanding the aux battery charging system

Cheers

 

Yes, it is about 99% SOC, and as I told you, your monitor is not reliable on SOC estimates. You should disregard its SOC estimates and should use it only for the voltage and temperature readings. Last but not least, there is absolutely no reason to shift to park at red lights, which is doing nothing for the 12-V battery but causing wear and tear on the transmission.

Here is the SOC-vs.-voltage chart for AGM and flooded-cell lead–acid batteries:

 

What does park mode do to harm the transmission? The pawl almost silently clicks in and out. Maybe yours is defective. I am not the one who got stuck with a dead battery. Nice big charts, again. Will continue on as before, with the more complete tech data, thank you.

 

Good information. Thanks for taking time to post.

 

Nice, I hadn't read this before. So, the rested open-circuit voltage is 12.36 V or less? This would be about 76% SOC or less. You could already have some 12-V-battery capacity degradation.

I will report on how the AGM battery works. It is arriving today, and I should be able to install it in the weekend.

This is the info in the Gen 4 Prius Prime new-car features manual:

CHARGING CONTROL

SYSTEM CONTROL

(a) This system is controlled by the hybrid vehicle control ECU.

(b) This system controls the voltage in order to maintain the capacity of the auxiliary battery optimal condition, then reduces the power consumption of the vehicle by controlling generated voltage of DC-DC converter.
1. The hybrid vehicle control ECU detects the electric load (inverter water pump assembly, oil pump with motor assembly, battery cooling blower assembly, engine state, etc.).
2. The battery sensor (battery state sensor assembly) detects the voltage, current, temperature and capacity of the auxiliary battery and sends a signal to the hybrid vehicle control ECU. Based on the signal, the hybrid vehicle control ECU judges the condition of the auxiliary battery.
3. Based on the electric load and condition of the auxiliary battery, the hybrid vehicle control ECU calculates the request voltage and sends the request voltage signal to the DC-DC converter.

FUNCTION

(a) The hybrid vehicle control ECU receives signals such as the charging/discharging current detected by the battery sensor (battery state sensor assembly) via LIN communication. Based on the signal, the hybrid vehicle control ECU calculates conditions such as the auxiliary battery capacity.

(b) The battery sensor (battery state sensor assembly) detects the auxiliary battery temperature and sends a signal to the hybrid vehicle control ECU, and the hybrid vehicle control ECU judges the condition to enter constant voltage control mode.

FAIL-SAFE

(a) The hybrid vehicle control ECU stops charging control and the DC-DC converter switches to the constant voltage control mode under the following conditions:

CONDITIONS INTENTION

When auxiliary battery capacity has decreased
When auxiliary battery temperature is low or high

When the condition of the auxiliary battery is bad, charging control is suspended to prevent a decrease in auxiliary battery charge. If the auxiliary battery temperature is too low or too high, the auxiliary battery capacity and lifespan may decrease.​

When the vehicle cooling system load is high
When the engine load is high

To avoid discomfort caused by voltage fluctuations in the power supply (maintain saleability and provide stable power)​

When a battery sensor (battery state sensor assembly) is malfunctioning
When voltage sensing is abnormal

When there is a sensor malfunction, charging control is suspended to prevent a decrease in auxiliary battery charge.​

When there is a LIN communication error between the hybrid vehicle control ECU and battery sensor (battery state sensor assembly)

When there is a LIN communication error between the hybrid vehicle control ECU and battery sensor (battery state sensor assembly), charging control is suspended to prevent a decrease in auxiliary battery charge.​

 

Roy Peterson, post: 3479374, member: 211800
"The TSB which I believe is a potential root cause of aux battery depletion is available on this forum."
I have not been able to find the TSB on this forum.
Can you point me at it ?

 

Gokhan:
Is the Gen 4 12v battery an AGM Battery ?
The Gen 5 is a lead acid flood battery.

 

No, Gen 4 and Gen 5 OEM batteries are identical GS Yuasa flooded-cell batteries, albeit Gen 5 battery having a central-vent lid with two vent holes for trunk installation so that you could plug one hole and connect the other one to the vent tube.

 

Did I read your post wrong ?
Are you installing an AGM battery in Gen 4 (12v battery).

 

Now, after all, this could be why Gen 4 and Gen 5 batteries tend to fail often. The battery is being fully charged only every 20 driving hours, which could be once a month or once every other month for an average driver.

In the past, the typical car battery used to last for ten years without any voltage control.