My new Prius Prime electrical system would not turn on at start up

There’s lots of threads here on 5th gen Prius with the plug-in having discharged 12 volt batteries, . One possibility is due to leaving the high voltage cable plugged in for a protracted period after charging; the car seems to keep monitoring stuff, running the 12 volt battery down in the process.

 

Does Prius do over the air updates yet? Haven't been able to find anything to that effect.

 

no, but why would that matter?

 

search is your friend:

621253265

 

That's like telling people to read the owner's manual... It just ain't gonna happen.

 

He means that perhaps you could solve the battery-drain problem with a software update, like the battery-drain problem for iPhones.

This is actually a good idea. While probably there is little a software update can do to reduce the drain, it could have pop-up warnings to the owner, such as "lights draining the battery," "AC cable plugged in for too long," "battery level getting too low—keep the car in the READY mode at least for an hour," "check for third-party accessories draining the battery," etc. Such warnings could reduce the number of instances of 12-V-battery drain tremendously.

 

The car needs to be driven regularly for long distances. The 12-V battery only charges when the car is in the READY mode. You could charge it through the lithium-ion battery (if it has charge) by switching the car to the READY mode in the EV mode, even without driving the car. You could also do that in the HV mode, but that's not recommended as it would fill the garage with exhaust fumes.

Also, do not leave the AC charger plugged in for longer than overnight. That drains the 12-V battery.

Not leaving the lights on unless the car is in the READY mode is also important.

 

You probably have a bad 12V battery. That would be confirmed if after doing all the suggestions, it happens again. Just so you're prepared, your dealer will probably say the battery checks out fine. They may even try to convince you that it's all on you, either something you're doing or something you're not. Testing the voltage output right after bringing it to full charge is not an adequate test. Another member had a frustrating experience when the dealer told them several times the battery was good. The problem was the battery would not hold a charge after sitting for while like a couple days or even overnight.

Hopefully, it doesn't happen again. But if it does, I would insist on a new replacement battery.

 

I’ve read that a car fully “on” but just sitting idling may still tax the 12 volt battery more than charging. Pretty sure this was for non-hybrid vehicles, though.

If disconnection of hybrid battery charge cable is not practical, having a smart charger hooked up to the 12 volt might prevent it draining.

No kidding.

 

I understand this is a problem for older Prius and needs to be addressed this way... But in 2024 they still can't send enough charge to the 12v? Total nonsense!

 

I am not sure what you mean by fully on, as that is not a technical term for Gen 4/Gen 5 Prius/Prius Prime. I believe there are four modes: off, acc, on, and ready. In the READY mode, the 12-V battery is always charged to near 100% SOC, as the DC converter is on, regardless of the drive mode (HV/EV) or if the vehicle is parked or driven or if the ICE is running or not.