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

My battery tested at dealer and with my equipment showed @350 CCA for a 285 CCA battery. If you don't drive the car for a day or more, the no load voltage drops from parasitic current drain. I have noted that occasiionally at night, the voltage spikes down few a few minutes for reasons I don't know.

 

Well, you can't really measure the CCA using cheap equipment. For one thing, you would have to refrigerate the battery.

 

Toyota dealer uses a fairly sophisticated battery tester. It provides a printout with details regarding battery condition, etc. Not sure what the equipment costs them. I have no concern regarding the condition of my battery. I tested with my electronic tester (Topdon) plus a tester that loads the battery for 130 amps for 10 secs. All good. I feel certain my dead aux battery back in august was due to the condition described in the TSB.

 

In any case, for the CCA measurement, you need to refrigerate the battery to the specified temperature.

 

I wonder if this is the computer phoning home for software updates?

 

Thank You !

 

Are there easily obtained obd scanners that read the battery sensor data?

 

NOTE: Also posted this in the Technical Forum

Yesterday, I charged the 12 volt battery with my Topodon charger in REPAIR mode. I believe this helps to possibly de-sulfate the battery. It took about 8 hours and ended with the battery reading 12.9 volts while on the charger at the end of the repair mode. Removed the charger and checked the battery voltage several hours later with my BT battery monitor. Voltage reading 12.79 volts. This morning I checked the battery voltage and it read 12.71 volts. Typically, I have been seeing a loss of less than 0.1 volt for an overnight. This would be expected from the dark or parasitic current that is constantly there. Toyota states a dark current of 120 milliamps or less is acceptable as part of their fault isolation procedure for a depleted aux battery.

Made multiple trips this morning. The first trip was short (about 10 minutes) and the battery voltage read 14.1 volts for 7 minutes of driving then decreased to 12.8 volts. The next trip was 14 minutes and I noted the battery voltage read 14.1 volts for about a minute then decreased to 12.8 volts. Basically same scenario on return trip. Summarizing, the battery voltage was at 12.8 volts for estimated 85 percent of my driving. After arriving home, let car sit for a few hours and then checked battery voltage to be stabilized at 12.57 volts. My experience has been that the battery voltage, i.e., charging voltage, while driving is predominantly at 12.8 volts from all my multiple observations. 12.8 volts is basically a battery maintain charge and I don't see it ever getting the battery to what would be considered a full charge.

I know from experience that very time you open the power hatch or a door the car wakes up and a drain on the battery for 10 minutes or more. I have confirmed this using an amp clamp on the negative battery terminal. If the headlights come on at car shutdown, the drain on the battery is quite significant. Thus, I no longer use auto mode for the lights. For my car, the last test I did indicated about 80 milliamps draw with the car asleep. This would account for the battery voltage slightly decreasing overnight.

One feature that sold me on the Prime was the ability to make short trips in EV mode. Looks like, from my experience, the aux battery system may not be up to the task. The number of dead aux battery complaints I feel is significant based on the low volume of primes sold to date. Toyota has a lot on their plate these days with multiple recalls across their offerings. Their corporate debt load is significant. The Tundra engine replacement costs are going to be monumental. The TSB for the prime cars regarding the depletion of aux battery if cable left plugged in is a puzzler. The use the term SOME cars. Well how do they know for sure that any car still could be affected ? The procedure in the TSB for the tech to determine the anomaly exists is not very clear as i read it. The warranty labor for the ECU firmware is 0.7 hours. I don't understand why Toyota didn't make it applicable for all Prime vehicles since the number of Prime cars delivered to date is relatively small. Pocket change in my opinion......

Cheers

 

The behaviour is consistent with the stuff from New Car Features and discussion in the other thread.

What you need to realise is that - like the traction battery - it's not aiming for totally full - it's aiming for what it considers "full".

It appears that they've fitted a 55Ah battery rather than the previous 45Ah of the Gen 4, and it seems they're targetting around 80% SoC of the 55Ah, which would be the about the same amount of charge as a totally-full 45Ah. But they will apparently occasionally charge it fully - every 20 hours of driving. (Would be interesting to see if you can instrument that).

So there is a method in their madness. You don't need to be worried that the battery is not being charged - it just isn't being charged to full most of the time. As to what this does to battery lifetime, I can't say.

 

Again, your conjecture is quite wrong.

First of all, Gen 4 and Gen 5 batteries are identical, except for the central-vent lid on Gen 5's for trunk installation. They are both 45-Ah. I have never seen a 55-Ah battery in the EN LN1 size. They are typically 50-Ah; so, the OEM-battery capacity is on the low side.

Help: Need Photos of Gen5 Prius 12volt | PriusChat

The new-car features manual explains that the battery is not fully charged to improve the fuel efficiency. The reason for that is that a lower DC–DC-converter output voltage results in a lower 12-V-system power loss. And that's one reason why the Gen 4 and Gen 5 batteries have been failing often. Setting an SOC target lower than 100% has nothing to do with battery capacity.

Lithium-ion batteries do not like 100% SOC, which results in battery degrading during storage. However, lead–acid batteries do—in fact, they do not like less than 100% SOC. This is not to say that you want to keep them at 100% SOC at all times even when the battery is being used—because that would result in increased cycling degradation when the battery is in use—but for storage, you definitely want 100% SOC.

Yes, the same problems exist in Gen 4, especially for Gen 4 Prius Prime. The battery-control algorithm is the same. Gen 4 and Gen 5 are quite similar cars.

 

In general, lead acid batteries last longer when stored at 100%. They'll also last longer the shallower the discharge per cycle. Discharge it less before charging, and it will give more cycles before needing replacement.

BU-201: How does the Lead Acid Battery Work? - Battery University
BU-804: How to Prolong Lead-acid Batteries - Battery University

 

Here's some data to digest from my car operational experience regarding the aux battery and charging system.

Yesterday evening, per my BT battery monitor, battery voltage was 12.57 volts. Early this morning, voltage was 12.52 volts. About 3 hours later, 12.51 volts. Drove car on 2 short trips. First trip the charging voltage was 14.2 volts and then 2 minutes later dropped to 12.8 volts. Trip length 6.6 miles and @ 12 minutes. Return trip charging voltage showed 14.2 volts on car start and then decreased to 12.8 volts less than a minute. Allowing car to go to sleep, battery voltage now 12.46 volts. From my experience in my situation, the car battery voltage will eventually hover in the 12.3 to 12.4 volts range. Thus it appears that the charging voltage I see of 12.8 volts will result in the battery in the 12.3 to 12.4 volts for my car and how I drive it. Most of my trips are 20 minutes and under.

It is what it is.......still love the car -

Cheers

 

In my case of a dead aux battery, I believe it is related to the possible depletion of the battery if leaving the charging cable attached after car finished charging per the TSB Toyota released in June 2024. The only time I had a dead battery was when I left the cable attached for a long time. However, unable to convince dealer to update the firmware per the TSB warranty provision. I have a level 2 charger so the car typically is charged 3-4 hours. I left the cable attached for a pretty long time thinking it was no big deal.

I don't believe the tech was made aware of the TSB (which I gave to the SA) nor did he do a proper diagnosis. Almost willing to pay for the TSB if I felt this dealer was competent to do the upgrade.

Cheers

 

Well, the new AGM battery (after having been fully charged with a Noco Genius) as well as the BM2 battery monitor are in.

First impressions: The battery sensor is extremely accurate within 0.01 V (checked by a precision multimeter). The car is doing a great job adjusting the battery voltage. It charges at 14.1 V and floats at 12.92 V. Since an AGM battery charges five times faster than a flooded-cell battery, I think I will get great results.

I think the car's charging system is actually very good. However, I also think that it is a good idea to invest in a cheap Noco Genius and to charge the battery occasionally.

With the help of the Noco Genius, my OEM battery probably still had four more years in it, but oh, well…

I will start a new thread on the AGM battery.

 

Which AGM did you purchase ? I see myself doing similar based on how it works for you

Cheers

 

Uplus EN LN1 AGM battery on Amazon

 

I just ordered one from Amazon. I think the AGM is best option for my driving scenarios

Cheers

 

It is a very high-quality battery made by a Singapore company that is an OEM manufacturer for major car companies, and it is deeply discounted at the moment, possibly because it is being sold directly by the company and/or they are trying to newly enter the US market.

It comes with a black barbed plug to plug the unused vent hole. You need to press it in with a socket driver or such, as it is too hard to press it in with your finger. I plugged the hole on the negative side in my Gen 4 Prius Prime, even though Gen 4 engine-bay installation doesn't have a vent-exhaust tube for the hole on the other side; so, I could have left both holes unplugged. But it will be safer without hydrogen gas on that side because that is the side that generates sparks when you disconnect the negative terminal first.

 

Also, it is crucial to fully charge it with a Noco Genius charger before you first install it in the car so that the battery management system in the car recalibrates itself properly. Leave it connected to the charger until the green LED becomes solid (not slowly flashing), which could take up to two days. The cheap Noco Genius 1 would work. If you already have a battery charger, you could use it as well, but in any case, it should have a dedicated (not automatic) AGM mode and you should manually set it in the AGM mode.

 

Thanks. I do have a charger with dedicated AGM mode. On purchase of new batteries, I always charge before install. Often the vehicles charging system will not get battery fully charged.

side note this afternoon. 16 minute trip in HV mode. Charging voltage stayed at 14.1 volts.

Cheers