Parasitic battery drain?

SW to 'Load Shed'. It's not that hard. Shut off RF receivers when the 12V battery reaches X Volts. It's not rocket surgery.
If it's a hybrid/EV they could power up the HV battery to charge up the 12V when required,
down to X Volts on the HV battery. Easy Peasy.

 

Just editorial: are you intentionally fracturing that idiom?

 

It's not as easy as you make it. It's easy in concept, but can get insanely difficult in execution. The problem is all the computer code in a modern vehicle. In the old days, most all of the computer systems were in separate channels(so to speak). Today they're in complex communication networks(CANBUS in general terms, Multiplex Communication System in Toyota-speak). I think it's safe to say a typical car today has millions of lines of code between all the different systems.

So what will happen is some errant line of code in some subsystem will have an unintended effect in some other system. Tracking down that line of code might be an absolute nightmare. And the problem gets far worse if it's an intermittent problem that only occurs when some weird combination of events happens. It can be like looking for a needle in a field of haystacks.

I also bet it sometimes happens when code is reused from previous versions of the system. Say they brought over some code from the 4th gen Prius on some subsystem that wasn't changed for the 5th gen. It worked just fine on the 4th gen, but on the 5th gen maybe there's a different new subsystem somewhere else on the car that interacts with it in a very slightly different way that causes a problem no one predicted.

And problems like these have the added fun of pitting teams of engineers against each other. The software team will blame the electrical engineers, saying the design of the circuits is faulty. The EE team will blame the software team, saying the code is faulty. And both design teams will blame the assembly line or the parts suppliers, saying the manufacturing or assembly is to blame.

 

Got my Consumer Reports April car issue in the mail yesterday.

Toyota Prius is #11 on the reliability ranking among hundreds of cars—so, it is excellent in reliability. Least reliable? Fords, Nissans, GMs, Jeeps.

The most satisfying car: Chevrolet Corvette. (Perhaps those who buy the Gen 5 Prius because they think it’s sporty should consider that. )

The least satisfying car: Jeep Grand Cherokee PHEV.

 

There is no problem at all with the Prius 12-V battery or parasitic drain if (1) the battery is fully charged at the purchase using a battery maintainer (ask the dealer to do that before they deliver the car if you don’t have a garage) and (2) if the car is driven for 40 minutes or longer in a single day at least once a week (if not, consider using the taxi service instead of buying a car).

So, there you go—your workaround has been fully answered.

 

What would I do without you...

 

You are asking Google to define problems that don’t exist and then asking for a solution for problems that don’t exist. That’s why it didn’t get you anywhere.

Few owners have actually fully quantitatively investigated this issue using a battery monitor. I am probably the only one.

The Gen 4/Gen 5 parasitic drain is 2.5% SOC a day—typical of a modern car. The maximum charging cycle (at 14.3 V without interruption) runs for 40 minutes once the SOC drops below 70% (it does not if it is above 70%), but it should be run in a single day, as otherwise, the BMS gives up.

The other issue is that many Priuses already come with a low SOC from the dealer. Since the maximum BMS charging is limited to 40 minutes and a single day (it does not repeat the next day), manual charging is necessary for deeply drained batteries, including during the dealer predelivery service, which most dealers neglect. A deeply drained battery and the insufficient charging of the BMS (combined with driving habits) results in a feedback cycle that further drains the battery and eventually results in a fully drained battery.

So, there you have it: the actual problem and its solution. It is not the parasitic drain. It is the BMS.

 

Poor Toyota....
I guess they're doom to be: The auto manufacturer that sells cars that can't be left unused for over X amount of days.

That's YOUR workaround.
"40 minutes or longer" ??? I'm out. And so are most commuters.

If this is not Clearly Stated in the Owner's Manual, and, in the Presale Prep list'o things to do.....
You're left with: cars that can't be left unused for over X amount of days.

Owner to service advisor: I had my car towed here because it will not power up.
Service advisor to Owner: You can't leave your car unused for over X amount of days. You must change your life style or buy a workaround solution, like Gokhan uses.
Owner: Is any of this in the owner's manual?
Advisor: Next customer, please.

"It is the BMS"

This is probably the best statement for this problem with the Gen5!
It's not Brain Science...

It's not difficult to maintain a healthy charge on a 12V battery. Every car with one has to do it.
Back in the day, (and now), when cars had alternators, after cranking up the engine the 12V battery was hit with a big surge of charging Amps, (60A?) which quickly lowers to maintain the 12V at the normal 13.8 to 14.2V range. It was easy. Batteries lasted many years. Cars could be left for long periods of time.
Yes, some didn't have: key fob receivers, cellular connections, wifi connections, BUT some do.

My '17 EV @ 127k mi. has the original 12V, partially because Hybrid/EV's give the 12V battery an easy life.
A 20A inrush to boot up the car and immediately the DC-DC converter is doing all the work and the 12V battery is just along for the ride. That's how it should be with any Hybrid/EV.

With this problem on the Gen5's, it's not the SW in the entire vehicle connected through the CAN bus. It could be just a small dedicated 12V battery BMS box the size of a deck of cards with the duty to stop feeding the RF receivers and save enough capacity in the 12V to boot up the car.
Imagine coming back to a Gen5 after a 4 month sabbatical and,, ta da,,, ! the car boots up!
Other cars can do this.

Some more advanced Hybrids and EV's will bring the HV pack online to power the DC to DC converter and charge the 12V, when required, while parked, unplugged for a long time.

The fact that a Prime can't be left plugged in, (such as in the dead of winter when you want TMS for the HV pack), is UNEXCEPTABLE.

Why not complain?

I may be interested in a new Prime when my Gen3 finally buys the farm...
But not until this UNEXCEPTABLE problem is solved.

 

In older cars without a BMS (like @Mendel Leisk’s Gen 3 Prius that he is familiar with), the 12-V battery sees 14.3 V at all times and, therefore, charged at all times when the car is running, remaining at 100% SOC.

In modern cars with a BMS—the Gen 4/Gen 5 Prius not being unusual in this area—the 12-V battery is not charged at most times. Toyota says in the new-car features manual that this is to improve the fuel economy. The BMS charges the 12-V battery only for a few minutes during the start-up and then only if the SOC falls below 70%. On top of that, its charging algorithm is buggy and prone to causing the battery SOC to drop over time by neglecting charging.

 

1. Same as it ever was. Back when 12V batteries lasted a long time, regardless if it's in a Gasser or Hybrid. And,, ta, da, you could leave your car for days and weeks unused.

2. Bunk on the 'fuel economy'.
Once a Lead Acid battery is brought up to the traditional (temp dependent) 13.8 - 14.2V range it takes hardly any current to maintain that SOC. It's such a small trickle that I'm not sure how that could be expressed in 'MPG'. And what about battery life when it's not charge up completely? I would think that suffers.

I guess it's back to the drawing board for this simple system of charging the 12V in a car.

 

Don't forget that Gokhan does not have, nor has he tested a G5. It's something of a leap to assume that whatever behaviour he's seeing in his G4 is the same in the G5, especially if the G4 behaviour is bad enough to be portrayed as "buggy". If it was causing problems from 2016-2022 they would likely have tried to improve things in the next generation.

Most of the problems we've seen from actual G5 owners look more like "something getting stuck and consuming too much power" problems. Which we've had at least one TSB for, for plug-ins.

(FWIW, I've had no problems yet, touch wood, but then my usage pattern probably wouldn't suffer from a battery management flaw. Maybe been left a few times for a couple of days plugged in at -20C, or a week and a half at 0C, but otherwise used for short tips most days, with long trips every other week.)

 

My G4 Prime in California started to charge normally every day if temps go lower than 45 deg F overnight appx. Now it warmed and the same old non charging starts again.

 

@Roy Peterson has been testing his Gen 5 Prius Prime while I have been testing my Gen 4 Prius Prime using a battery monitor, and we have been observing an identical BMS behavior down to the smallest details in every respect in our cars.

Moreover, an equal-number or more Gen 5 Prius/Prius Prime owners as Gen 4 owners have been having 12-V-battery issues (as you can see from many threads here).

There is one difference though: The Gen 5 Prius Prime charges the 12-V battery during plug-in charging (until the charging is complete) using the DC–DC converter. The Gen 4 Prius Prime does not but keeps it at a float voltage of about 13.0 V (until the charging is complete) using the auxiliary DC–DC converter in the charger, which is only capable of providing a small current, and it is mainly to run the electronics without draining the battery. The Gen 5 Prius Prime does not have an auxiliary DC–DC converter in the charger.

As I have said repeatedly, you will be fine if (1) the 12-V battery did not come with a low SOC from the dealer and (2) the car is kept in the ready mode (driven or stopped) for at least 40 minutes in a single day for at least once a week. Stop doing (2), and you could start having battery issues. I never had battery issues either until I had repeated six-week-long vacations.

 

When did you move to California?

 

Those cars with no electronics whatsoever are long gone. Even the brand-new 12-V battery in my brand-new 2009 Corolla died when I left the car undriven for a month. They don’t make them like they used to. LOL