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).

 

The DC–DC converter also turns on when the traction battery is charging. The voltage could be as low as about 12.86 V, but according to @Roy Peterson, it is as high as about 14.1 V in Gen 5, which is the aggressive-charging voltage. So, apparently, Gen 5 is improved over Gen 4 in that the DC–DC converter actually aggressively charges the 12-V battery during traction-battery charging—according to Roy. In Gen 4, you don't see more than about 1–2% SOC increase for the 12-V battery during a traction-battery charging session. Moreover, when the traction battery is charged, keeping the car plugged in will increase the parasitic drain in either generation due to the charging computer staying on until the car is unplugged.

 

If a car comes with the solar cell roof, does that charging trigger the parasitic drain?

Re-routing it to the 12 volt as a built in battery tender would seem more useful than adding its meager contribution to the traction battery.

 

It shouldn't. When the car is charging the traction battery, the 12V system is receiving power too.

The problems early cars had with the battery seem to be linked something not going to sleep when it should and perhaps a batch of bad batteries.

 

With retirement, then Covid, our Prius (2010) was seeing much less use. For a while I used the same rationale, driving for semi-neceessary reasons, but mostly just to keep the battery charged.

Then started thinking, how purely tail-wagging-the-dog this was. We do have the convenience of a garage with AC outlets, and this doesn't work for someone street-parked. but any time the car's going to be idle a few days (which is most of the time), I connect our smart charger, and just leave it on.

We do need the car maybe once a week, sometimes more or less, and the drives are good length.

 

This is nuts. Pay 50k Euro for a car and have to fiddle about keeping the battery charged!!

 

100%!