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

I'm pretty sure other manufacturers figured this out.
The 12V is monitored, Load Shedding begins at X SOC. When necessary turn on the DC-DC to transfer X amount of Whs to the 12V.
Monitor the HV pack. Give up the ghost, throw your hands in the air, at 40% SOC, (months later?)
It's not Rocket Surgery

Again, I changed out my +8 year old Bolt 12V battery because I got tired of waiting for symptoms. Did GM figure it out?

 

The Gen 4 and Gen 5 Priuses have no 12-V battery issues when properly maintained, and their 12-V batteries will last 10 years or longer, too. You don’t fix something that is not broken. Besides, Toyota engineers know what they are doing. Every Toyota technical manual, whether it is for Prius or not, instructs that the battery must be fully manually charged if it is drained (due to not having been driven, etc.), which is the only reason for the failure.

 

1* What does 'properly maintained' mean to the typical owner? Some word of mouth extra procedures?
2* A 'Technical Manual'...? Does the typical owner know any of this by reading the Owner's Manual?

I understand that you have brand loyalty and appear to be an apologist for this Problem.

Is this the problem?
You can't leave your PHEV plugged in after it has charged to 100%.
You can't leave your PHEV while gone on a +2 week vaca? Or any combination of those?

I really don't know. No skin in the game. But there sure are a lot of reports and questions on this and other related threads.
From here, it looks like if the hardware could support it, a simple SW update would make this 12V system play nice, just like any other EV and PHEV.
You seem to have studied this system for a long time and might know why a SW update can't be done.
What about a hardware and SW update? And toyota foots the bill?

 

After finding my 12 volt consistently sitting at less than 50% state of charge, I’ve unplugged sensor on the negative terminal of the 12 volt battery. This fixes the charging voltage at 14.3 volts whenever the car is in “Ready” mode. It doesn’t light up any warnings and now my Prius keeps the 12 volt topped up just like most other vehicles.

I did the same thing with my 2014 F150 after the first battery lasted less than 3 years, with no adverse effects. The second battery lasted 7 years.

I don’t think that Toyota can do anything because additional 12 volt charging would lower fuel economy slightly and require new testing, reporting and affect CAFE ratings, etc.

 

Is this a Prime only or Warm Weather phenomenon for the HEVs?
I've only had my HEV since November, so not that warm yet.
I've been keeping my eye on voltage, and it's always 14.3-14.4 v in Ready.
Time will tell I guess.

 

Or, alternatively, hook up a Noco Genius every three months or so.

The 12-V BMS keeps my AGM battery between 75–90% SOC, which is OK. I would definitely hook up the Noco Genius if the car is not driven for over a week. The temperatures are never too cold here for the car to automatically turn off the BMS. I see no reason to manually cancel the BMS (by disconnecting the sensor) in my case.

Canceling the 12-V BMS may actually reduce the 12-V battery’s lifespan by increasing the number of charge and discharge cycles. I believe the 75–90% SOC target chosen by Toyota is optimal for battery longevity, while also improving fuel economy and decreasing greenhouse gas emissions.