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

You have been saying the same thing for Gen 4 for many years now.

 

Agreed. There was a serious discharge problem with gen 4 for some owners, same as gen 5.
It’s like the gen 3 head gasket issue, some have it and some don’t, but no one knows the cause

 

And just like the 12-V-battery issue, the Gen 3 head-gasket issue was due to owner error. If you trash your engine while you drive it, don't change the coolant, etc., don't expect your head gasket to last forever. Likewise, if you use the ACC mode, keep the lights on when the car is not in the ready mode, don't do frequent long trips, keep the car plugged in when not needed, etc., don't expect the 12-V battery to survive for too long.

 

You’re making wild assumptions and accusations in both cases without any evidence

 

i realize, many think they know

 

Toyota might.

Our third gen's battery more-or-less living on a smart charger, will be 9 years old in september. Load tests like new still. I kinda wonder if I quit with the charger, it'd be like the proverbial Portrait of Dorian Grey.

 

Does Toyota disconnect the 12 volt for no reason on all the Priuses shipped from Japan?

 

And what have you been making?

@Salamander_King, a previous Gen 4 Prius Prime owner, agrees with me.

 

How do they drive them on and off ships and around the ports with a disconnected 12-V battery?

 

I’m going by what I’ve read, please link sals agreeable post

 

I don't want to be dragged into this... but you must... All I said was "many cases, it is an operator error"... Certainly I believe there are some defective batteries and installation errors involved. But the dying 12v battery issue is far more beyond just for Prius. It is for almost all modern cars having many electronics running when the car is off. And it is more aggravated in hybrids with small 12v battery. Yet, it is not universal problem in all owners, so there are certainly user case variables that plays a role. That is all I said and it is 100% personal opinion only, no data or evidence to back it up. So, I certainly would not generalize it to ALL cases of the 12v battery failures.

 

Sorry Sal, but thank you

 

Which is more or less what I have been saying. Of course there are always going to be defective parts and isolated failures, not with just 12-V batteries but any car part.

But it is not an inherent design flaw by Toyota, as @bisco has been religiously claiming. As you said, newer cars, especially hybrids and even more so plug-in hybrids have high drains on the 12-V batteries, and the owners neglecting to do frequent long trips, using the ACC mode, leaving the lights on when the car is not in the ready more, leaving the car plugged in when not needed as if it is a smartphone, etc. will most definitely result in 12-V-battery failures. So, it is not a problem unique to Gen 4/Gen 5 Toyota Prius/Prime, and the owners need to realize not to be oblivious about what is going on with their 12-V system.

Perhaps the only remedy is a fast-charging 12-V system equipped with an LFP 12-V battery. That will solve the problem of owners doing only short trips, as it would charge the 12-V battery in minutes as opposed to hours, which would in turn solve the problem of the 12-V batteries failing from sulfation due to extended periods of a low SOC. In fact, lithium-ion batteries, unlike lead–acid batteries, like a low SOC. But that won't happen at least until Gen 6. So, till then, stop complaining and learn how to use your car, which is far more productive.

 

Please link where I said it was a design flaw on gen 4.
On gen 5, some owners said it was a software issue which an update fixed

 

What we know for sure is that some gen 5 and 4 owners had 12v issues that they didn’t have with their previous gen Prius.
Some went so far as to document the voltage drain over time.
Yes, some were due to owner error and others were not.

 

Note, the 'not universal' nature doesn't rule out a lot of batteries being bad, nor a car issue that only triggers under certain conditions.

Toyota should know what the car off load on the battery is. If they install a too small battery that results in a deep discharge on start up after the car has been parked overnight, then yes, that is a design flaw.

 

As I said previously, I left my 2021 Prius Prime Limited undriven for over six weeks in hot weather with an active full Toyota Connect subscription last summer. The 12-V battery still had no problem starting the car. I should add that it was fully charged before I left it, as I always do long trips at least four times a week.

So, the drain is larger than your grandfather's car, but it is not beyond what the system can handle. However, it is an entirely different story when the car doesn't see frequent long trips, kept in the ACC mode, lights kept on not in the ready mode, charger is plugged in for longer than overnight, etc. Then, the car no longer gets a chance to recharge the battery more than it is being drained, and the 12-V battery often sees a low SOC, which eventually results in sulfation and battery failure. A larger-capacity battery is unlikely to solve the problem if the owner's habits are chronic, as the battery would still eventually end up in a low SOC with a negative balance on charging/discharging. The only likely solution is a fast-charging 12-V system with an LFP 12-V battery, which can even charge with owners with chronic habits, such as driving the car for mostly short trips.

Previous Prius generations probably handled short trips only etc. better because (1) they had less electronics with less 12-V drain and (2) AGM batteries can tolerate a low SOC that would eventually result in sulfation better.

 

Toyota should have increased battery capacity commensurate with drain

 

As an electrical engineer, having a traction battery charger drain the 12V battery (however slowly) while it's plugged in is just sloppy design. Toyota has been making PHEVs long enough to know their customers are going to do what is most convenient. They are going to plug it in until the next time that they use the car. Whether it is 1 day or 3 months should be irrelevant. Expecting that the user will babysit this so the 12V battery isn't drained is not how engineers are trained. We're trained to design things to be "idiot resilient". If Toyota is marketing the car for more "mainstream" users, then they need to design it to that standard.

Shoot, it would cost at most $10-15 to add a small circuit to the traction charger in the trunk to keep the 12V charged anytime the car is plugged in (yes, I know there already is one that charges while in ready mode, but clearly this isn't adequate). This alone would help mitigate some of the other weak 12V battery issues by keeping it charged while it sits in the garage.