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

Agreed. My bolt recommends leaving it plugged in when not in use.
It keeps both batteries conditioned that way

 

They use a connected battery.
https://static.nhtsa.gov/odi/tsbs/2020/MC-10178779-9999.pdf

 

What makes a long trip, and how frequent, for keeping the 12V charged?

The annual car mileage in Japan is under 7000km, or well under 5000 miles. If this was mostly an issue of the owners not taking proper care of the 12V, it would seem there would be a lot of dead ones there.

There seems to be a case where the software isn't putting a system into sleep mode under certain conditions. Though I think that bad batch of batteries played a part. Whether they were bad from a defect or improper storage doesn't matter.

Owner's manuals provide two things; important information for the operator, and a CYA for the manufacturer. I believe the warning Toyota gave about the 12V battery and charging is the latter.

The 12V is charged while the traction pack is being charged, the battery heater is own, and whenever else the car calls for power from the outlet. The addition drain happens when power isn't called for, as the system monitoring for the conditions to call for power. Keeping the charge cord depowered when not needed is a safety feature.

Other EV makers have 'maintain the 12V' as a reason for the car to draw power from the outlet. Some even will do so from their traction pack when not plugged in. Toyota likely also do so, but the drain over a couple days likely isn't enough to be a concern. That is until other issues with the 12V are present.

You got a like for keeping it polite.

 

This is why the traction battery charger should have circuitry to know the status of the 12V battery and include a charger. The charge cord should remain powered until both batteries are satisfied. While the charge cord is plugged in, this charge circuit should check both batteries at least once each day to see if they need to be topped off. The 12V can power this and would only need a few micro-amps if done properly.

Option 2 is the traction battery always keeps the 12V battery maintained as long as the car is plugged in whether it's charging and the cord is energized or not. If the car is unused and still plugged in, the traction charger may need to pump the main battery up when it drops below 95%, but it's not going to be very often.

This isn't a challenging nut to crack.

 

Isn't this an SOP for any Toyota?

 

What about level 2 charging where there are two hots and a ground, and no neutral? I don’t think any maker has cracked this nut yet. Maybe Hyundai and it was something different.

I don’t know. I just saw the reason they disconnect the 12 v after securing the vehicle, then reconnecting on unloading is to prevent possible discharge on the cars in the bulletin. Does it matter?

 

Your previous post singled out the Priuses and the OP's and some others' claim was that the Prius had a specific problem.

That said, it looks like that is indeed an SOP for any Toyota, not specific to the Prius:

https://static.nhtsa.gov/odi/tsbs/2021/MC-10201302-9999.pdf

 

I guess I'm not understanding your point. The onboard traction charger can handle 120V or 240V input and it's galvanically isolated, so the hard work is already done. Adding a small 12V trickle charger and monitor circuit would cost Toyota no more than $10 - $15 using automotive grade components.

 

Doesn't even need that. Just a software update to power up and supply current through the DC to DC converter. It is what some others do. But the extra draw while plugged in likely minor, and only becomes a problem for batteries that are already damaged.

 

I am thinking if a 120 v to 12 v charger is simply added, on 240 v the ground wire acts as the neutral. The load on each leg is different by adding the charger. But the acting neutral, which is the ground wire also, is bonded to every receptacle and sub panel in the building. Not up to code. Neutrals are only bonded at the service panel.

 

First you were laughing at cars driving off the ships with batteries disconnected as if it wasn’t true that they do disconnect them. Now you search and find out the 2022 Camry hybrid from Japan also has the battery disconnected. Stands to reason it does. They give the same reason, possible discharge. They load them, pull out the fuse, put fuse back in, unload them. Then do the recalibrations needed. They did yours too.

 

You are the one who made the blunder by cherry-picking and singling out the Priuses, not me.

It is all Toyotas, not just the Prius HEV/Prius Prime PHEV and Camry HEV. If you look carefully, it lists both the nonhybrid and hybrid Camry models.

Do you know what Ro–Ro means? It means roll on, roll off. I was merely asking how they drove the cars on and off the Ro–Ros and around the ports with the 12-V battery disconnected. So, they perhaps disconnect the battery after it arrives at the final delivery point or perhaps they don't. OK—for whatever this information is worth.

 

120V is hot, neutral, and ground. 240V is hot, hot, and ground in the case of a 3 terminal connection and hot, hot, neutral, and ground in the case of a 4 terminal. In all cases, a ground reference is provided and is what is needed to be code compliant.

The traction battery charger has a universal input which means it first has a boost switching stage to bring the voltage up to 300+V (this also provides active power factoring). Incidentally, this is one reason the charger is more efficient at 240V vs 120V because there is less loss boosting from 240V to 300+V than starting at 120V. After that, is the buck stage which provides isolation and brings the voltage back down to the various needed DC rails. One of these rails would power the 12V charger.

All the "hard stuff" is already in place. Worst case is they need to add a few turns on the PSU transformer to create a new 15V DC rail. I suspect there may already be one in place since that is a fairly popular voltage used with MOSFET switch drivers.

All this to say that they were 98% of the way there whether they solved it with proper hardware or a firmware work around. I don't know why they didn't take the time to properly test and mitigate something which has bitten them in the past. There are no excuses for this.

 

Well you imagine a lot. I sent our two cars to Hawaii and some years later sent them back.
Toyota disconnects the battery in Japan after the car is secured down. Then the person at the port puts the fuse back in and drives the car out. They state because of possible battery discharge.
I didn’t make any blunders, or cherry pick anything.

 

This has been suggested and discussed many times by many others for many years since long before Gen 5. The ultimate engineering design and safety rests on Toyota's shoulders, not ours. Toyota is well aware of this, but they have reasons not to do what you suggested.

In any case, as long as the car sees regular long trips (they don't have to be that long, on average, perhaps fifteen minutes of driving per day should be sufficient), the car is not kept in the ACC mode, the lights not kept on unless in the ready mode, the AC charger not plugged in for longer than overnight, etc., there won't be any problem.

It could also be that many of those who are having a problem have hidden accessories or perhaps hidden dealer tracking devices that are draining the 12-V battery.

So, the long story short, I don't think there is even a problem to begin with.

Speaking of dealer tracking devices, my 2009 Corolla XLE that wasn't being driven regularly had a dealer tracking device I asked to be removed when I bought the car, which probably wasn't removed. It had a 12-V battery failure when the car was about a-year-old, which now I think that may be because of that device.

 

The "DC Cut" fuse is removed during delivery shipping (on all Toyotas). That doesn't totally disconnect the battery - it removes power from a lot of auxiliary functions to reduce drain. And it's fully driveable with that fuse removed. On initial delivery the dealer would reinstall it, as per the document above. After it's been driven off the ship and whatever else it was loaded onto on the way to the dealer.

 

Send Toyota a message and maybe they will either explain it or offer you money on the spot for the idea. I know three wire clothes dryers and ranges are no longer code compliant because the ground has to be used as the neutral for the 120 volt equipment in the appliance. Since the J1772 is three wire for supply, I was assuming it must be more like a simple electric wall heater that doesn’t need a neutral inside the charger. That’s what I was writing before.

 

That makes sense. It hadn't made sense how the 12-V battery could be entirely disconnected through a 25-A fuse.

 

We don't know if this is causing the issue. From those that got batteries replaced under warranty, it doesn't appear to be.

 

I wondered about that as soon as I read it. Now who is volunteering to take the fuse out and start driving to test? Not me.