Will the hybrid battery charge the 12V battery when car is turned off?

"Design flaw" is a subjective opinion,
and it not up to anyone to declare it incorrect.

 

A damaged box is not the same as tapping some power to boost a battery.

 

Had jumper cables in "every" car I've ever had since my first in 1976...including my current hybrids and ZR1. If I need to jump it, I either f-cked up, didn't drive it for to long or there was/is a problem that I address/ed. YMMV.

 

Jumper cables or a portable jumper box work, but they are not ideal. It would be better if the car could utilize a little bit of power from the hybrid battery when you press the start button. Instead of disabling the car and requiring a boost or a service call.

 

Paul,

I have owned Prii for 21 years and have never had an issue with the 12v battery. I keep track of battery health and only replaced one when it was 8 years old and appeared to be weakening. If you are concerned, get a battery maintainer and hook it up when your Prius will be idle for more than a few days. I have kept a portable jumper in my Prius, but have only used it to help other people.

Prii are not perfect, but Gen2, Gen4 and perhaps Gen5 Prii (I left out Gen3 due to their engine issues) are very good, well designed cars.

JeffD

 

Some EVs do do this. Well, actually, they monitor 12V system voltage while off, and if it drops too low reconnect the traction battery to top it off. The question is if it is worth the cost with the much smaller traction battery? Besides the cost of the feature, is it worth the extra strain on the traction battery to keep a potentially failing 12V charged up?

There are at least two hybrids that do have a self jumping feature for the starter; the Ioniq and gen1 Niro. They don't have a lead acid 12 though, but is a portion of the traction pack. So relay tripping required, just a switch in the software.

Likely originated with an outside standards organization, such as the SAE. My guess is that it started among the EV1 era EVs.

 

Of course the risk in that might be a continual drain off the hybrid battery with a constant parasitic drain over time, which is probably why it was designed to keep the hybrid battery isolated. But a little more thought into the design might do the sensing before the 12V battery goes completely dead, and it should keep topping up the 12V battery with a sufficient charge to operate the sensing circuit. If this continues over a long period of time, it could run the hybrid battery flat as well, so the sensing circuit should then isolate the hybrid battery from further discharge.

Owing to the enormous capacity of the hybrid battery, this occurrence would be relatively rare, and would require a boost. But this would be much more favorable than the overnight drain that many of us experience with the current design, requiring either a boost or a service call.

 

Regulation and standards are always way behind innovation. That's the reason we can't have those European headlamp control systems; they run afoul of US standards regulations - even though they're safer and offer a larger field of view at night.

YMMV

 

Yet European regulation managed to allow those lights on the roads. Our lack of access from lagging regs isn't the regulations' fault.