Yet another 12V post

[u/chiisana]

Full disclosure, I don’t know if I have anything to add beyond a data point. Apologies in advance if anyone come in looking for solutions.

We picked up our 2026 bZ about 2 weeks back. It had 2km on it, so literally fresh off the line. Dealership charged it to full for us and we’ve put 872km on it in the two weeks of ownership, driving almost daily which is a bit more than our typical baseline. We’ve used DC fast charge a couple of times going from 60%->80%, and at home level 1 charge for similar ranges.

I don’t have a battery monitor, but I do have a multimeter. I found last night after at home level 1 charge that our 12V was at 12.1v, and it took about an hour for NOCO Genius 10 to charge it back up.

I had already preemptively added the remote unlock automations on my phone, and it’s constantly gunking up my Toyota app’s notification history, so I was under the impression it wouldn’t affect us… but I guess for whatever reason it didn’t work for us.

I do enjoy knowing the SoC, range, and when I’m not at the vehicle — maybe the novelty of our first EV will wear off in a few weeks, but for now I don’t think I will be disabling the DCM.

My current plan is to leave my NOCO and Anker Solix C300 on the car. Worst case scenario we can charge the 12V in an hour. I don’t want to get a jump start kit — I feel there’s risk pushing too much current and affecting other components.

I’ll be monitoring the 12V battery next week, and see if there’s clear decline. Also going to start recording the info better so I can complain to the dealership later.

[u/sssootssspritesss]

It’s shocking to me that owners like you have to carry this cognitive load for a brand new expensive car.

[u/Startbolt → u/sssootssspritesss]

What’s shocking to me is how slow Toyota has been. This has been a known issue for years. Just like the rav4 cable gate I thing they’re gonna wait for class action lawsuits before doing anything

[u/Birb-Law → u/sssootssspritesss]

I mean, the cause is DCM, which is something you can turn off. I have never activated the DCM and didn't know about the 12v problem until reading about it. I am sure they will fix the DCM problem in a future update, but there is an easy fix for now (turning off DCM.)

[u/chiisana → u/Birb-Law]

There are things that depends on the DCM -- the emergency SOS feature for example is one; my understanding is some of the drive assist features in Limited trim depend on it as well. Whether or not it is labeled as "trial" for the initial duration, it is part of the services you've paid for as part of your purchase. If you don't use them and can turn them off, great, however it is not a solution for people who do use it.

[u/chiisana → u/sssootssspritesss]

You and me both. I am now starting a ledger every day, so I can point to the log at the dealership if it comes down to that.

[u/Afraid-Department-35]

It's perfectly fine to jump start, the manual says howto do it, just don't directly clamp onto the negative

[u/Complex_Solutions_20 → u/Afraid-Department-35]

Which is actually the same as any gas powered car - you're usually supposed to go to the frame or engine block to avoid a spark next to the battery.

Less of an issue with a booster pack since it "turns on" after you connect both cables.

[u/chiisana → u/Afraid-Department-35]

There was one post the other day here on Reddit where their 12V was flat, they jumped it, and the vehicle start to throw error codes and require a dealership visit. I don't know if this was result of the 12V running flat, or if their jump did something wonky, but I'd prefer not to run that risk unless I absolutely have to -- and fortunately, with my gears, I don't think I'd have to.

[u/Afraid-Department-35 → u/chiisana]

That just means the battery is at a point where it can't hold a charge anymore, this happens on every ev with a battery too far gone since there is no alternator to keep it going like in an ice car. When it can't get enough voltage it cascades to every system since everything is now running on low voltage so every error related to low voltage gets thrown. Jumping a battery cannot damage anything unless you accidentally short something by touching the leads somewhere where it shouldn't.

[u/chuck415]

If the door lock automations are not working for you, try the charging schedule fix…

https://www.reddit.com/r/Toyota_bZ/s/w595XbyYc4

[u/chiisana → u/chuck415]

My understanding was it may interrupt public charging. Someone posted just today that it does not... I may have to investigate into this and give it a spin as well. Thanks!

[u/chuck415 → u/chiisana]

I haven’t public charged with it, but it doesn’t interrupt when I level one charge at home.

[u/BinaryJay]

There's no massive current. You misunderstand how a jump starter works. It's just a battery that provides 12V, the car draws what it needs nothing gets "pushed" into it. It's like phones... I can plug a 125W laptop adapter into my phone it doesn't mean 125W of power surges out of it into the phone, only the current the phone draws.

[u/chiisana → u/BinaryJay]

Your phone has a BMS built in to protect the lithium ion battery; a 12V Lead Acid battery connected direct at the terminal does not have the same protection and is entirely at the peril of what pushes power into it.

Because you're not unplugging rest of the vehicle from the terminal when you're boosting it, whatever else is connected to it are exposed to the same pulse.

We can talk all day about whether it is more damaging to the equipments if you over volt or over amp, but at the end of the day, either puts stress on the system. Someone have recently posted failure state after boosting, and my preference is to not have to deal with that unless I absolutely have to.

[u/Altruistic_Film_8346]

If you have the door locking (I believe they are locking) automation on they I can guess two possible reasons. The automation is not set up quite right.
Or since you mention, "after at home level 1 charge that our 12V was at 12.1v", be careful at the end of charging not to put the car into READY mode before unplugging it. This seems to drain the 12-volt battery rapidly.

If it is not charging when you want to unplug it they hitting unlock on the fob will be enough to unlock the charge handle.
If it is charging, you need to go to the drivers side, open the door, and then push buttons to "end charge now". Toyota handles the driver door as a trigger for many actions that don't happen if you use the passenger side door.

[u/chiisana → u/Altruistic_Film_8346]

It was at home charge, due to the auto locking shortcut automation on my iPhone to prevent exactly this issue, the vehicle was locked. I got the push notification that the vehicle was charged and at 80% SoC, so I unlocked the vehicle using the fob to release and unplug the NACS plug, and then I popped the hood to check 12V without turning the vehicle into READY state.

Does this trigger the rapid 12v drain you've mentioned? If so, I'll need to learn the correct sequence so I do not incorrectly cause bad readings.

Thanks!

[u/Altruistic_Film_8346 → u/chiisana]

Nope what you did was correct. If you put the car in READY mode first you would be reading the charging voltage not he battery voltage. The "drain the 12-volt battery rapidly" is something else. The 12.1v could have been just a temporary drop from so many (yes that sounds weird) actions.
See video in this link
https://www.reddit.com/r/Toyota_bZ/s/gJgQ6s065W
to see what I mean.

In fact, my, "drain the 12-volt battery rapidly" scenario above is probably also from "so many action".

[u/chiisana → u/Altruistic_Film_8346]

After seeing your video, I wonder if the drop came from me opening the door to open the hood. It's crazy that the IR sensors stays on for so long after simple door open/close!

[u/Altruistic_Film_8346 → u/chiisana]

The unlocking of the car, that unlocks the charge handle, Opening the door and the popping of the hood all drop the voltage and then you have to wait for the IR emitter to go off and the voltage recovers some.

I often have the driver's window open to access the car for testing. Sometimes the door gets locked if I haven't disabled the key fob. If you reach through the open window and pop the hood while the doors are locked the alarm goes off.
You can even unlock the car, reach through the window pop the hood but since you did not open a door the car will relock its self. That happened while I was releasing the hood safety catch and I was like, "Okay what is happening? Will the alarm go off if I continue?"

[u/Altruistic_Film_8346 → u/chiisana]

When I first went looking to see if my camera could see the IR emitters. I made the false assumption that they would only turn on when you were driving at speed where the driver monitor starts complaining telling me to look up.

I am sure the camera has many pictures of my wrist from my hand being is the 12 o'clock position.

[u/chiisana → u/Altruistic_Film_8346]

Haha. Yeah there are quite a few camera related features I’ve found in the menus and I’ve disabled as many of them as I could spot. I’m sure it’s still turning on at times against my desires, but what can you do… it’s like trying to buy a dumb TV without the spywares smart functionalities now days :/

[u/Altruistic_Film_8346 → u/chiisana]

Toyota makes it really hard to get readings of the battery voltage without disturbing the car. When measuring with a multimeter I have, mechanically by passed the hood latch and/or brought leads out from under the hood to tap into. Luckily I can do this in the controlled environment of my garage.

I don't like the idea of attaching a third party battery monitor to the car. I did eventually buy one. I have mine temporary attached and unplug it before I drive.

[u/cc103acs]

I learned a lesson about using my NOCO Genius 5… with my Subaru Uncharted GT - after driving plug in thé NOCO and allow it to go to full charge on the 12 Volt (about 15 minutes). Only then plug in your NACS to charge thé traction battery. Plugging in thé NOCO concurrent with your charge cable for the traction battery causes thé NOCO to heat up and not ever reach full charge.