2024 Prius Prime dead battery

First of all, since your 12-V-battery SOC neared zero, it resulted in sulfation and permanent capacity loss. This is irreversible. Keep that in mind.

The problem is that the Gen 4/Gen 5 Prius/Prius Prime battery-management system likes to keep the SOC around 70–90% and won’t charge the battery much no matter how long you drive the car except once in every 20 driving hours. This could sometimes result in the SOC getting too low. Therefore, the only way to eliminate 12-V-battery problems on Gen 4/Gen 5 Priuses/Prius Primes is to periodically use a battery maintainer (such as Noco Genius) to bring the SOC to 100%.

AGM battery for Gen 4/Gen 5 Prius/Prius Prime and observations on the 12-V charging system | PriusChat

 

Search the site using google to discover the many gen 5 12 volt battery issues.

the 12v only boots the ecu’s and closes relays. It does not start the engine.
That task is performed by the hybrid battery, so no need to run in charge mode

 

That is correct. There will be a significant but very brief current draw (perhaps 50 A or more and for about a second) from the 12-V battery during the starting to fire up the electronics, but there is no need to put the car in the HV mode or charge mode, as it is the DC–DC converter that charges the 12-V battery, and the DC–DC converter is agnostic to the selection of the HV/EV/charge mode, as it is powered by the traction battery, not the engine.

 

Do you think there is a way to change the programming of the 12 volt charging? It should always try to charge to 100%, like old cars do. It wouldn’t cause extra traction battery use in the simple way to look at it. What is the savings to keep the 12 v 70-90? It still is replacing all the lost charge from the 12 v either way. No more or less with either.
Could it be the Toyota system is so primitive it doesn’t stop charging like a 1964 Plymouth alternator/regulator would? I may try and see if the dc converter ever turns off charging when car is in park. I always see charging, never “charged”.
I remember the P2 never stopped charging? Don’t remember exactly. Then the Camry hybrid added a temp sensor which must work to stop charging. Now we have this battery sensor thing.

 

the pip kept the 12v fully charged. prime engineers made a conscience decision not to, you'd have to ask them why.
change the programming; anything is possible, no one here has the technical knowledge to pull it off.
and so many things are proprietary with toyota, it would be a difficult task for the best software guru.

 

So you agree that the only way to eliminate battery problems in a Gen 5 is to use a battery maintainer to bring the SOC to 100% ?

 

With my Uplus AGM battery in My Gen 4 Prius Prime, I’ve been observing the next-day resting voltage, and so far, it has not fallen below 12.71 V, which is 85%. So, there is no need to hook up to the battery maintainer at the moment. However, I will definitely do so if I don’t drive the car for more than a few days.

 

I don’t think there is a simple way.

Interestingly, the Gen 5 new-car features manual mentions that when the 12-V-system load is high, the DC–DC converter produces the maximum voltage [14.24 V] to avoid a system instability. For example, I see this when I use the electric power steering brought to the stops. The voltage will rise to 14.24 V when the steering wheel is brought to the stops, and it will stay there for ten or twenty seconds or longer even after the steering wheel is brought back to the center.

I am still waiting to see when the next once-in-every-20-driving-hours fully charging event will take place—perhaps this week.

 

a week ago on November 9 I went out to try and start my Prius and it wouldn’t. The display flickered a few times with spurious faults, and that was it.

to give Toyota roadside credit. Someone was there within an hour to boost it

The car had been sitting in the garage for about two weeks un driven, and the symptoms sounded a lot like what other people have reported here.

so I called the dealership on Monday. Their reaction was yep we’ve heard of this before and within a week I had the battery replaced under warranty (it did fail a test) and since the car was in, I also had the rear door lock recall performed.

So for people talking about battery minders etc. I would suggest you go to your dealership first and have them check the battery particularly if it’s the one that came in the car, if you haven’t already done so.

 

I think the only difference is you are now starting with a new True Start USA made battery instead of starting with a new made in Japan battery. If you do the same things, it should be the same result, dead battery.

 

I went from 2 to 4. My daughters Camry hybrid original Panasonic 12 v lasted 15 years. Now she maintainers the new $265 one, discounted price, almost every night. Backs into garage and plugs maintainer in. Noco 4. Expensive 12 volt for that car.

 

It’s definitely possible. I see the logic in your statement… unless it was an issue with the battery ITSELF.

I can’t figure out from the multiple threads if people who HAVE had a battery replaced under warranty have had the same issue with the replacement battery.

Of course, they may have changed their behaviour.

Speaking for myself, I’m not going to leave the Prius with charging hooked up if i think i won’t be using it.

Thought that feels quite counterintuitive.

 

from what i have read, it seems there are a couple different problems, which makes deciding what to do in the future difficult.

 

Contemplating the future battery in my 2024 TOY PP XSE, I'd really like to try the Ohmmu LiFePO4 battery. It comes with a bluetooth app you can install on your phone and monitor battery voltage, current, power, and SOC. Would be great for seeing exactly what the '24 Toy BMS is doing with the battery as you use the car. Answer many of the questions I have about the cars BMS.
Only thing is that LiFePO4 batteries accept very high current under charging conditions. And I'm not sure what SOC the Toy BMS would try and keep the LFePO4 battery at. LiFePO4's do not ever have to be charged to 100% SOC, but at low charging voltages their SOC is effected and they may not provide the same power (Watt-hours) to the vehicle when parked and subject to passive battery loads as a lead acid battery at 70-80% soc.

-Does anyone know the 12v max current rating of the '24 PP Toy Traction battery DC to12v battery/system DC device (charger/converter) ?

 

This is actually quite normal with any modern car, especially a Gen 4/Gen 5 Prius/Prius Prime. You don’t want to leave the car undriven for more than a few days without connecting a battery maintainer. The parasitic drain is several percent everyday, and you could have the battery drained fast, and two weeks is already stretching it.

So, the long story short, get a Noco or similar battery maintainer and hook it up when you are not driving the car for more than a few days. And also hook it up a few times a year even when the car is driven regularly to bring the SOC to 100% and prevent or reduce sulfation.

So, @bisco, no, it is a very easy decision: Get a battery monitor and use it when the car is not driven, and use it a few times a year even when the car is driven regularly, given how the charging system in Gen 4/Gen 5 lets the 12-V-battery SOC drop and doesn’t charge it aggressively.

And, yes, GS Yuasa vs. Toyota TrueStart won’t make a difference.

Regarding the battery type, an AGM battery is an improvement over a flooded-cell battery, as the former charges more easily and can take deeper discharges, but it won’t make the problems disappear, especially if the car is left undriven.

I don’t know if an LFP 12-V battery with its own battery-management system would work. if you try it, let us know. It might not, given how the Gen 4/Gen 5 battery-management system behaves.

 

Same thing happened to me after owning the car (2024 Prime xse premium) for 2 weeks. I took it to the dealer and at first was told if nothing was found, I would be charged! Nothing showed up on the computer but I wasn't ultimately charged.