12V battery died again

Your profile says 2018. Is this a Gen5?

Anyway, I have an '26 HEV, but I just went out, started the car, put it in Park with the radio on and went inside the house for a while. The battery monitor shows it was charging when in Park. Only for a few minutes though, I didn't let it go for a long time.

The only time I got that message was when I was fooling around with my dashcam on Accessory. It wasn't too long either, so it's pretty sensitive.

I cut and pasted a couple of things from my manual.

This is probably a PHEV specific thing, I bet.

 

Probably this one:
Prime Main Forum (2017-2022) | PriusChat

 

Have you checked your battery voltage with a meter or ever replaced your 12V battery? Using a volt meter will tell you, if your system is working properly. Car OFF should read 12.xV, car ON at least 13.8V+. If your car isn't doing that; there's a problem with your DC-DC converter or your not in "READY" mode. If you was actually in "READY" mode, there's NO way the battery could've slid under 12V. Even if your traction battery ran low; the car's ECU would've turned-ON the ICE, same as it would while your driving. Have you ever replaced the OEM battery from 2018, it's 8 years old and probably on it's last legs. Get a free check at any auto parts store.
There's also a misconception that there is a 12V maintenance charge while the car is plugged-in. That is WRONG; the 12V maintenance charge is ONLY ON while the traction battery is ACTIVELY charging. If your read your OM; it states to unplug your car after the traction battery is fully charge; otherwise the car will actually drain your 12V battery by doing more internal readiness testing.

FWIW; the car will start with the battery all the way down to around 10.75V; but it may start throwing phantom error codes due to lack of power.

IMHO; testing is the only way to nail-down an issue. Guessing usually doesn't solve anything. Good Luck....

 

was there something about gen 4 that wouldn't let you camp in it because it shuts down after a certain time?

 

Since I've retired; I've noticed my battery hovering around 12V or just below - now that it isn't a daily driver. It's never stranded me or failed to start; but I do keep an eye on it's level and place it on a 6A charge for a few hours a couple times a year. This gets the battery back up to 12.5+V - where it should always reside. I do unplug after the traction battery fully charges; though sometimes the next morning.

Hope this helps......

I don't believe the 20 minute auto-shut-off limitation applies to the gen4 Prime - don't know for sure, never tested that. If it does apply, the simple work-around would be to set your parking brakes and throw the car into N. This serves two purposes, If the car isn't in "ready" mode - the car won't go into N. You KNOW your in ACC mode and NOT Ready. You need to be careful though, because you can easily bump the car into D. This shouldn't be an issue, if your parking brakes is set and your not on the "gas pedal".

 

my experience with the Gen4 Prime in READY mode for around 30 minutes, CD playing, ( in HV mode, so the engine can switch on if the system calls for it to) is that the (hybrid - big- battery) looses charge slowly 1/10 mile worth at a time on the dash gauge. I never looked at the 12 volt reading on any of the apps I have on my phone that show it during those times.
My cars 12 volt system typically shows the 12 volt readings of around 12.2 - 12.3 after the first push of the ( READY button ) and 14.1 volts after the second push of the READY button. YMMV

There are modes and/or settings combinations that will drain the 12 volt system !
@ChapmanF can explain the technical details of why the Toyota Hybrid Synergy Drive system behaves that way.
If I recall correctly A/C on in HV mode and neutral gear is the Big one ! 10 volts in less than 1 minute..