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

Purchased Sept 2023 and no issues with 12 volt. I'm in California and we have time of
day charging hours that are more expensive so I unplug when the rates go up so car is
never plugged in the entire day. I make it a point to drive it twice a week even if I don't need to since my
2017 12 volt died after a month being idle in the garage.

 

Ditto. Recently had it sit for 16 days without loss of charge.

 

All your answers are in my post. Please read it.

 

I can remove all trace of that mod in 5 mins anyhow.

 

I can't say if my battery is now draining or not. I plug in the maintainer the minute I get home.
But I can say that the first few months were a nightmare regarding my 12 V battery constantly draining too low.
My Gen 3 would always start up, even if the 12V battery fell to 10.5 volts. My Gen 5 refuses to start with anything below 11.5.

 

Again, you have been looking at the DC–DC-converter voltage, not the battery open-circuit voltage after rest.

 

I'll keep doing that. It makes me feel better

 

I hear you.

 

I work with non-Toyota Ev’s. Every one of our models had issues with 12V batteries dying. Software updates fixed the problem. I’m sure one is in the work for the Prime. Leaving the charger plugged in all night should not be an issue. If it is currently and issue, it can and will be fixed with firmware update.

 

It is just that modern cars use 12-V-battery-managament systems, and they don't like to keep the battery fully charged, which increases the risk of battery failures and decreases the battery lifespan. For most people, the battery lasts for four or more years, but for some others, the miserly battery-management system combined with other factors causes early failures. So, the battery-management system is not optimized for battery longevity but fuel economy.

 

I recognise your experience. Who apart from you has a portable battery charger?? Toyota need to fix this, yesterday!

 

Thanks for this. In my researches it seems many hybrids have this achillees heel - not only Toyota. Toyota would boost my confidence by admitting the problem and working on a fix instead of asking whether I left the lights on!

 

I'm finding my battery drain to be quite variable. As far as I can tell, the DC-DC converter is not engaging while the car is off.

 

True, it does not engage for charging if the car is not in the ready mode (on).