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

Yes, the true solution is to figure out why the batteries are dying in the first place. However, that still doesn't address the laundry list of user "don'ts" that Gokhan outlined. The only way to attempt to cover all those is to ensure the 12V system stays topped off whenever the car is plugged in (again, whether or not the traction battery is actively charging).

As for why they didn't choose to design around this problem, I suspect they figured it wouldn't bite them. Someone has chosen poorly....

 

they're sellingmore than they can make. so obviously...

 

SIGH...I know. The bean counters win again.

 

Most of the things on that list, ex. "leave lights off", are things for any car. The people having issues seem to have to made sure that wasn't the case.
The warning about the drain on the 12V while plugged in, where is it in the manual? It has been quoted here, but I didn't see it in the after charging section. They do warn not to leave it plugged in for a long time to avoid dirt, dust, and water building up around the plug. If the 12V going flat in such a time was a problem, shouldn't it be mentioned there?

 

Is this from the wiring diagram, or what? So if it is fully drivable why not just take the fuse out? What aux items are turned off? They said in the bulletin there is a way to recalibrate the intelligent sonar by driving. I would like to learn that if it is in the service manual.
Plus how to test the 12 volt battery sensor on the neg terminal.
Would be good info for the site.

 

You could add a function to keep the 12V battery topped off whenever plugged in. But that would only help plug-in owners when the car happens to be plugged in. It would be an auxiliary function benefiting a subset of people, and not necessarily the people who need it.

(My personal nice-to-have in the same area of leveraging the plug-in would be powering the engine block heater from the plug-in socket, so I didn't have to connect a second connector. They could have done that too.)

Adding a "top up the battery from the mains" function is a thing you could do to save the battery, but it's niche, targetting a supposed potential "flat battery while plugged in" problem. Topping it up from the traction battery or having some automatic "do the equivalent of DC cut" relay triggered by low voltage.would be more general.

Yes, it's in the wiring diagrams, obviously. And it's described in the bulletin. Basically it cuts most of the power supplies for OFF or ACC, leaving READY supplies unaffected.

There was a post here where someone had blown ECU-DCC No. 2, which is downstream of DC Cut - he lists all his symptoms. DC Cut would have killed all this and a bit more.

(His radio and multimedia and wireless charger were also always dead, but that could have been due to a blown Radio fuse. But that might also be covered by DC Cut).

If you want to try to make your battery last longer when you're not using it, the DC Cut fuse is less trouble than fully disconnecting - it's specifically designed with that function. The only "why not" would be that a buggy power drain could conceivably be coming via another route? Probably not though - this basically kills all the smart computery bits, and it seems that whatever problem there is is likely an "ECC active when it shouldn't be" problem.

The sonar reinitialisation stuff was for G4. In G5 the only listed items to recalibrate are the driver powered seat, and the powered back door if it was open when the fuse was removed.

 

It says there is a way to recalibrate the sonar by driving method. Just for info, mine seems to work fine. I was also hoping to find the ohm value or whatever is required to test the battery sensor on the negative battery cable. I could spend $25 but if someone already has access to the service manuals, it would be good to share the testing procedure.
All this still leads to no one is removing the fuse every time they park. The cars still have a 12 v battery discharge problem, just as many other makes besides Toyota have. Like I wrote before, my 1998 Chrysler warned about leaving the vehicle over 21 days. I found that to be about right too. The difference is the alternator charges fast, but this Prius does not, it’s slow and inconsistent.
That's why I want to test the battery sensor. Maybe there was a bad batch of those, or even just a few.