Okay. Who HASN'T had a 12V battery issue with their 2023-24 Prime?

The Gen 4/Gen 5 12-V battery will usually be fine for most people if the car is driven regularly—meaning at least for one hour each time a few times a week. Keep in mind that the BMS keeps the battery at around 75%, which causes some sulfation. Also, the regular parasitic drain is about a 2.3% charge loss a day, which means that if you don't drive the car for longer than a week, you need to connect a battery maintainer or perhaps disconnect the battery. Also, if the car hasn't been driven for more than a week, it is a good idea to manually charge it with a battery maintainer to bring it back to health, as the BMS will never fully recharge it otherwise.

I didn't have any problems for four years, but eventually, my month-plus-long holidays without connecting a battery maintainer took their toll and completely drained the battery. It was still OK after manually recharging it though.

 

After the first dozen times, frustration sets in.
Besides, I like my solutions.

 

After a bad experience with my Gen 3, I am reluctant to let the battery go flat in my Gen 5.
I hooked up a boost, and nothing happened. I used a 100 amp booster-charger, and it made the relays rattle, while the panel lights blinked on and off. Eventually the car started, but I was worried about damage to the system until I sold it a few years later.

 

I just joined this club today with my 2024 prime 12v battery failing (dealer said it was in good health on Saturday - 10K maintenance). I jumped it using the fuse in the front. I'm going to get a Noco Genius5 to charge and maintain it. Can I attach that using the fuse in the front that is used to jumpstart the car? It's so much more convenient then getting to the battery in the trunk.

 

Having 'relays rattle' is not good for anything.
A better technique might be to connect the booster to the 12V battery and let it add current to the dead battery for a while.
Then hit the power button.

 

In retrospect, I should have disconnected the battery and put it on a charger, but there was no way to predict what happened.

 

It's not a fuse, it's a special contact for attaching a booster clip. But the best place to attach the NOCO battery maintainer is with a ring terminal on a threaded stud nearby, in the same fuse box. That's how I connected mine; I'd attach a photo if I had one.

 

I attached my NOCO maintainer directly to the battery in the trunk, using ring terminals on the battery's threaded terminals and existing nuts. The NOCO unit has mounting holes that allow it to be attached off to the side, just right of the trunk opening. The NOCO's power card can pass out of the trunk, and the trunk lid can then close on it with no damage to the trunk-lid gasket or the cord. I plug the NOCO device in whenever the car is parked at home.
I was at first afraid that I might someday drive off without remembering to unplug the device and stuff the cord back into the trunk. To prevent this, I have an object (a flashlight, but what it is doesn't matter) that I normally keep in the trunk but that I throw onto the front seat whenever I'm plugging the NOCO unit in.
Of course, every time I plug/unplug the NOCO unit I think about the incompetence of the Toyota engineers who are forcing me into these rituals.

 

Ahh, yes!
The JOY of having a modern PHEV from a major manufacturer.
One that requires you to dik around with plugging in the car twice when 'at home'.
Once with the safe J1772 for the HV battery, and once with a live extension cord for the 12V battery.

Hopefully this manufacturer will get things figured out before it finally has a BEV that people want.

 

Well, actually,,, the booster pack acts like a 'battery charger' when it has more voltage than the car's 12V battery.
The current flows from 'high to low'.
Allowing this 'flow' to add power to the 12V battery for a bit before drawing power from it for the boot up.

 

It’s part of life for other makes as well. Plenty of forums talking away about it. I have a few maintainers, one waterproof 4 amp Everstart from Walmart. It can be left out in the rain, has no settings, plug in and it works. The extension cord runs to a gfci and a couple times it was tripped as the end of cord was laying in the wet. Now I put the end under the car if it’s raining. Lately as temps went into forties the car has been charging the 12 volt much better.

 

More succinctly, a Toyota dealership? Good look with that.

 

Do you know a booster that doesn't work that way?

 

Sorry, I was replying to the post about 'Relays clattering'....
I was just trying to say,,,,,
"Maybe allow some time for the boost to feed the dead battery. The 'inrush' current is high for a while. Then try the Boot Up."

 

Of course you can't expect the Local Yocals to reengineer the SW controlling the 12V battery SOC. That's on Corporate.
Some cars can be left while you jet off on a winter's Vaca and not have to plug your car in twice.
I can leave my cars at the airport for 2 weeks without worrying about the 12V battery.

 

That seems obvious in retrospect, but when I was faced with a dead battery, a simple boost seemed in order.

 

Oh f course, but for people who might be considering this car and reading this thread , it looks like the car has all these problems and I just like to insert my experience and say I’ve been driving my car since August 2023 and I havent had a single problem with anything that I could blame on Toyota.

 

Has your car been driven daily during the time? Or close to it?

 

I have a west coast first boat 2023 prime SE, I have been left stranded 2wice so far, I may have contributed to the 1st one in 1/24 as the key was in my pocket while working near the car (locking & unlocking it)… not enough power to open the truck had to do the rear seat crawl, (at 70 that was a big ask)…. Dealer service adviser was a jerk (strike2) blaming me right out of the box while threatening to charge me if they could prove it my fault…. (Strike 1 was the $1000. Paint protection scam they tagged on the purchase, and Surprise!: after signing and paying cash they say you only get one key for now…. (that after the agreed to $3000. over msrp just to get an early one…)
Just yesterday it left us again (1/25), this time I could open the truck and put the charger on to get it to shift out of park and drive it… 12v battery toast this time and (different) dealer comp’d a new one.
We plug the car in every day programmed to charge 4 hrs overnight as we do drive it, though it can go a few days at times on the 240v cord not being driven, 12k miles and 7 stops for gas so far….
Mfr and programmers should be able to protect the traction and 12v batteries, its bullxxxx ask me to time and predict my usage and time my charging to baby the batteries…. These cars are an appliance and should operate as such…. Now my Miata? That’s not an appliance… and yes, we baby that one…
Chuck
Ps: this is my first post….
23 MX5 RF Club, 46 Chev 1/2 t

 

There’s no way being around the car with the fob should kill the battery.