HELP - 12v battery on backorder

When you had the problem when you put the car in accessory mode and you couldn't start the car after, was the car left unused for a long time, a light left on, or something else that drained the battery?

 

Battery is already at 12.35V. Nothing on in the car. Nothing plugged in except a USB cable that isn't connected to anything at the moment.

 

I guess, your next step would be to determine whether the drain is coming from the car or due to a bad battery? If you had another battery to swap, you could check to see if it holds the charge disconnected from the car. For a reference point, I checked my car this morning. It was back to 12.62v from 12.41v yesterday because I plugged in to charge the traction battery. I had a very short ~10miles drive I had to do today.

 

The reason I don't suspect a parasitic load is because the battery isn't going dead. If it was the car it would have to be drawing about 2A to go from 12.8V to 12.3V in 10 hours. The battery would be dead in 20 hours, but I can leave it sit for days and days and the battery isn't dead. Maybe there could be a parasitic load if the car cuts it off after the battery reaches a certain voltage.

 

I actually observed a similar phenomenon on my 2020 PP which sat on the driveway 1-2weeks in between drives. You can read it more on 12v Battery Is Discharging, Re-Charge Now! | Page 4 | PriusChat. To summarise, the fully charged battery lost ~0.1v/day for the first 3 days. But it stabilized at around 12.6v after the 4th day. It stays at around 12.6v after this and if the car is driven at least ~1hr and fully charged afterward once a week, then it replenishes the charge to full. If the car stays undriven for longer, then the battery will slowly discharge in 2-3weeks down to about 12.4v but I never saw lower within that time frame.

 

I can't suggest any place in Canada, but at least in the Eastern part of the US, I am not seeing the shortage of this battery. I just checked on the Toyota-online-dealer parts store portal. I found ~50 dealers with this battery in stock. I don't think they will ship to Canada, so this may not help you, but the Toyota battery (Part Number: 00544H4052470) is available. The lowest price I found was $135 + core charge (MSRP US$180.79+$17 core charge)

00544H4052470 - Vehicle Battery - Genuine Toyota Part

 

That spec on the battery case is: 20 hours of draw at 2.25 amps = 45 Ah rating.
This battery will probably not supply 45A for 1 hour. The 20 Hour Rate is a more realistic way to rate car batteries.

RC (Reserve Capacity) is a similar rating system where a set 25A is drawn from the battery down to 10.5V. RC is in minutes.

There are two ways of testing a battery:
Load test with the big cables going to a big heat producing resistor. You are looking for something close to the CCA rating.
Capacity test with a controlled load that, for example, maintains 10A and you are looking for a number close to the Ah rating.
10A from a 45Ah battery should last ~4.5 hrs to get to the 10.5V point and stop the testing.

(Aviation batteries get tested 'Cap Checked' yearly. You care about the Ahr rating for when the charging system fails and you rely on the battery to get you down out of the clouds and to an airport. Starting the engines is the second important thing a battery does.)

And then there are these new high tech battery testers with small cables and yet they will display a CCA number without actually putting a big load on the battery during a test. No idea how these work.... But they seem to be the standard of the industry now.

 

It had been in the 12.1-12.2 area for a while, maybe a month or two, when I was starting to keep an eye on it. At one point I thought I turned the car on to program some stuff through the OBD2 port but was in accessory for about 10 minutes. Then I got the low voltage warning, and couldn't even hold 12.1 volts after a full charge with an overnight maintenance charge. But after the repair, it's been holding at about 12.6.

 

Yes, this is similar to what I used (Ancel BA301). I have no idea how these work -- they seem like voodoo to me and I don't know how well you can really assess the "deep" health of a battery in a 1-2 second test. But these are becoming the standard, it seems, so they must be doing something right.

 

I have a hypothesis supported by preliminary data, but I have to do more testing to confirm. It appears that the 12V battery continues draining after a charging session even if the charger is disconnected.

This morning I completed a long drive and tested the voltage immediately upon parking. It was 12.80V. Over the course of the next 3 hours the voltage never changed. Then I charged the car for one hour and disconnected the charging cable and in the following hour the battery drained from 12.80V to 12.63V.

I intend a two-prong test of this hypothesis. First, I will repeat the experiment to confirm. If it looks like it's confirmed I will try putting the car in READY after a charging session and then turn the car back off and see if that halts the battery drain.

Wouldn't it be something if the 12V battery issues just turned out to be caused by the car sitting after charging?

 

At least for my 2020 PP, that did not happen. Here is another link from the same thread I have been using.
12v Battery Is Discharging, Re-Charge Now ! | Page 10 | PriusChat

In summary, during the traction battery charging, the 12v battery remained at a slightly elevated voltage of ~12.6v but did not fully charge the battery. It basically stayed the same voltage as before the charge session. The graph is a copy from the link above.


From this single result, I concluded that the charging traction battery does not charge the 12v battery much to increase the capacity. It only maintains it at the level of SoC before the charge session started.

HOWEVER, this conclusion may not be correct all the time. I never repeated the analyses on my 2020 PP again. With my current 2021 PP, I am seeing substantial charge-up of the 12v battery after the traction battery charge session. For example, 12.41v was charged up to 12.62v after the traction battery charge session just a few days ago. In fact one reading I took during the charge session while the traction battery was being charged, the 12v battery voltage read at the post was 13.63v. This can be explained only by the fact that plugging in the EVSE (L1 120v) and charging the traction battery was actively charging the 12v battery.

I may try installing the battery monitor on my 2021 PP to see again how the 12v battery voltage changes over time. The monitor will make it much easier to check the changes before, during, and after the traction charging sessions and other events such as ~1hr of driving.

 

Yeah, the second attempt did not yield the same results. It's never "that easy."

I would hope that the charging system isn't programmed to only feed the battery with the current voltage + some small offset unless that voltage is checked periodically throughout the charging process. For example, if the battery's at 12.1V and the charging system applies 12.5V at the beginning and never updates the voltage as the battery charges there will be problems.

 

I agree. The 12v battery charging system onboard a PP (and maybe Gen4 to some extent?) does not seem to follow a simple straightforward rule. It must be following some logic, but even during the READY mode, the charging 12v battery at 14.x Volt is not always constant. Similarly, I suspect the 12v battery charging during the traction battery charging session behaves differently from one session to the next. I will install my BlueTooth battery monitor on my car and attempt to collect more data. It makes it so much easier to have a continuous readout of the 12v battery without opening the hood. And if needed the data file can be exported into a spreadsheet for further analysis.

EDIT: I just installed the BlueTooth BatteryMonitor on the 12v battery of my 2021PP. The voltage was down to 12.38v as read by Fluke and right on exactly the same 12.38v with the BMII reporting. I will be charging the traction battery tonight. So, I can see the charging in process.

 

I decided to watch what happens when you start a charging session. It looks like the PP does some kind of current sensing to detect the SOC of the 12V battery and adjusts the charge based on that. When the session starts the voltage drops a bit and then quickly climbs to ~13.4V. It only stays there for a moment where it falls back down to 0.1V above the resting voltage.

 

Yes, that is the same observation I have seen with my Battery Monitor data. In most cases, when the 12v battery already has sufficient charges (although I do not know the exact cut-off voltage for this), the charging traction battery does not continue to charge the 12v battery during the charge session. Instead, it merely maintains the 12v battery at ~12.68v. What I do not know is that if the 12v battery is very low at the time the charge session starts, then how long it charges the 12v battery. It doe charge the 12v battery at ~13.48v instead during the charge session. This voltage is distinctly lower than ~14.4v the car uses to charge the 12v battery during "READY" mode.

 

I tried those testers over a decade ago; they were only correct about 15% of the time - whereas my bulky load tester was always correct. I don't know if those little boxes has improved over the years. I guess because they are small and convenient people use them.
The reason you can't get consistent readings off of those little boxes is that they're giving you an indirect measurement, based on the manufacturer's proprietary algorithm and the variations of the boxes internal components. IMHO: I consider them a random number generators and a crap-shoot. Sometimes less is more and a carbon pile load tester will tell you if the battery will start the car. If your not going to drive the car for more than two weeks; it should be on a battery tender - it's that simple.

 

I think they're better than just going on battery voltage. I mean, even a weak battery will show full voltage after its charged on a charger. I think it's just best to use common sense. If your battery is 5 years old and it goes dead on you and you didn't leave a light on or leave it plugged in for a couple of weeks or more without using the car, just replace it. It doesn't help that the car doesn't fully charge the battery, the battery is puny, and there seems to be a higher than normal parasitic drain especially when plugged in.

 

OK...I already have this...
ANCEL BA101 Professional 12V 100-2000 CCA 220AH Automotive Load Battery Tester Digital Analyzer Bad Cell Test

but I put this on my Christmas wish list...
Clore Automotive Solar 1874 500 Amp Carbon Pile Battery Load Tester

 

I had a battery in a Gen 1 Insight that tested good on a Load Tester outside an auto parts store.
The 3 second test....
But I'd still get a few times where it would not boot up the Insight's hybrid system. Had low voltage.
(This battery not used for the 12V starter motor, but it could in certain conditions.)
I put it on an aviation Capacity Tester and it fell flat on its face after <4 mins of a 20A load. I don't remember the RC or Ahr rating.

These are the two ways of measuring what a battery is capable of. Aside from the new magic boxes.

A home mechanic could come up with a Capacity Tester with headlights in parallel or some such load.
It wouldn't be constant current testing, like a real Cap Tester, but it would tell you how healthy the battery is.
Sort of a slightly decreasing Amp draw down to ~10.5V.

 

Possible contributor to 12v battery drain - at the 3:30 min mark in this video addresses an issue with a Data Communication module staying on. Supposedly a dealer software update fix.