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

Please just let this thread proceed normally without your intrusive interference.

 

Good grief, why don't you proceed normally then instead of telling people how you feel about them and name-calling them?

My reply to you was actually very nice, and you ignored its contents and didn't answer my question but resorted to name-calling instead.

 

Really, just keep driving superfluously, say twice as much as necessary, to counteract excessive draw?

Reading between the lines, they still haven’t disclosed the milliamperes?

“Trickle charger” (a misnomer) should be a smart charger, around 3~5 amp rating, that runs a charging regimen, and is capable of being left on indefinitely. It doesn’t matter if you hook up directly, at the under hood jump point; as long the wiring’s all solid there’s no difference.

On our Gen 3 we went by 100,000 kms Christmas Eve, and we’ve yet to make it to 101,000, 4.5 months later. That’s low usage. The 12 volt is an Optima Yellow Top, installed September of 2015. I’m using a CTEK 4.3 charger, pretty much constantly, with a permanent wired-in connection at the under-hood fuse box (battery in hatch).

Attached is a simple voltage check, about a week back, first thing in morning, day after driving. I also occasionally load-test it, but that’s more arduous, has to be right on the posts.

Anyway, maybe someone with a Gen 5 will do a phantom load test, clear this up.

 

Any car that requires frequent long trips is not fit for production

 

And the dumbest idea I've heard in a long time.

I think we were all getting along just fine, until I failed to take your "certain conclusions" at face value. Maybe I had my doubts or something, but it wasn't long before I was being labeled a "troll" and accused of being a liar about owning my Prius Prime. It's not that I doubted your "great wisdom" or anything like that, but I don't like to take anything at face value, and tend to look for a bit of corroboration elsewhere. If you are insulted by that, I suggest you may want to try to get over it.

 

No one ever verified excessive draw. However a bad battery was found.

Not quite.

 

I'll be able to verify excessive draw fairly easily, once I use the car for awhile. So far, I've had the car parked for over 15 hours without the battery maintainer, and the battery still seems fully charged, testing 12.6V at the battery, not far off where it was yesterday. I don't need to jump to any conclusions, but it looks like resetting the wireless networking module was the right move. The dealer didn't mention anything about phantom draw, so I don't know if they tested for it. It was nice of them to replace the battery, but it didn't seem to be the sole cause of the problem.

I've learned to be a bit skeptical of instant verdicts, so if that makes me appear to be a troll, I apologize.

 

I'm happy to report that my car started fine this morning, despite not being connected to the battery maintainer. Next phase is to see what happens over several days.

 

@Hammersmith, @bisco, et al., the following is what I have concluded. Perhaps I am wrong, but I think this is what has been happening:

Gen 4 and Gen 5 have a very high drain on the 12-V battery. It is worse for the Prius Prime than for the Prius, and it is worse for Gen 5 than it is for Gen 4. So, especially if you have a Gen 5 Prius Prime, you are in bad luck.

So, I think what is happening is that, unless you do long trips most days, avoid sitting in the car with the car not in the READY mode, avoid keeping the car plugged in unless it is necessary, and avoid similar battery-draining activities, the car cannot fully charge the battery. The battery charge gradually decreases over time, and you end up having a chronic condition of a low state of charge. Lead–acid batteries cannot stand a low state of charge for extended periods of time, and they die.

Note that a larger-capacity battery wouldn't solve the problem, and it could actually make it worse, as fully charging it would take even longer. Similarly, an AGM battery wouldn't solve the problem either, as they are mainly good at low self-discharge, and self-discharge is not the problem here.

Moreover, the problem becomes even worse if you purchase the car with the 12-V battery already in a low state of charge. Then, you could get only a few months of life out of the battery.

I think the only remedies are:

• Do frequent long trips, avoid keeping the car plugged in unnecessarily, avoid sitting in the car when not in the READY mode, and avoid anything (such as third-party accessories) that drains the 12-V battery.

Or

• Use a good trickle-charger.

There was one owner from Southern California (Huntington Beach?) who claimed that he only did long trips but his battery still died. I don't know what happened there.

@Paul Gregory, what brand of replacement battery did they use? GS Yuasa EN LN1, Toyota TrueStart DIN H4, or something else?

 

Don’t call it a trickle charger; the nomenclature police’ll be all over you.

It would be good for a few owners to test this.

 

And I disagree with that(Gokhan, not Mendel). But I could be wrong as well.

My theory is that the gen5 Prius Prime should be able to easily handle several weeks of non-use when it's functioning as the engineers designed it, even if it's been mostly used for short trips prior to the inactivity. I believe the problem is/was due to an unintended flaw in the software causing the car to behave in ways it wasn't designed to do.

My theory:

When the cars left the factory, the batteries were fine. But some part of the software either doesn't let the car completely go to sleep, keeps one part of the car awake when it's not supposed to be, or regularly wakes the car up from sleep unnecessarily. This effectively functions as an unplanned parasitic draw. Because the battery is a little smaller than it probably should be, the draw causes the battery to regularly slip into the danger zone where a depleted state causes damage to the battery. Cars that spent this last winter exposed to extreme cold weather suffered even more damage. Eventually, the damaged batteries couldn't even hold enough of a charge to last a couple days without going dead.

It's possible Toyota has already found and fixed the issue through an over the air(OTA) update, but that wouldn't completely solve the problem in cars where the battery has already been damaged. For those cars, the fix needs to be both the software update AND a replacement battery. It's also possible Toyota has not actually fixed the problem and replacing the battery will just be a temporary band-aid. We won't know until Toyota publicly addresses the issue or those with replacement batteries go at least a year without problems while also not using any kind of battery maintainer.

I also disagree that the larger replacement battery will make the problem worse rather than better. It appears the Prime deals with the 12V battery a little different than traditional cars. It seems to monitor the battery and only charge it when it depletes to a certain level. Then it charges it up as quick as it can to full, before waiting for it to discharge again. The trouble comes when the car is shut off when the battery is approaching the lower cutoff, but hasn't quite dropped low enough to trigger a charging cycle. Then the parasitic draw pulls it below the cutoff and keeps draining it down into damage territory. A larger battery will reduce the probability of the battery ending up near the bottom of the acceptable voltage range. It won't solve the problem, but it might buy time by giving a larger safety margin.

Ultimately, we may never know if either of us or neither of us are correct.

 

Reasonable speculation. I'm sure the answers will come as things unfold.
I believe the hunch that my system needed to be reset was a correct one. The dealer also believed this to be the cause of severe battery drain. I suppose there had been some damage to the battery, and I'm glad the third dealer decided to replace it. The first two had refused to do that.

Although it was a bit of pain to set everything up after the reset, the car is now performing to my expectations. There was no appreciable drain overnight. I don't think a few tenths of a volt are significant. I will still continue to use the battery maintainer, as I believe all Priuses are prone to some battery drain.

 

Requiring more regular, longish trips to maintain 12V battery charge is a really poor design choice for a car designed for Japan. Annual private car mileage there is barely over 4200 miles.

 

I've not measured it, but I don't believe the computer consumes large amounts of power. I believe the DC converter that serves as the 12V charging system provides adequate power to run 12V systems, and keeps the battery at optimum charge levels.
It seems unthinkable that the car would draw down the battery, and require the driver to run the car to charge it.

I think you should call a trickle charger a trickle charger,
and a battery maintainer a battery maintainer. They are not the same thing.
A trickle charger will degrade the battery and eventually destroy it.
A maintainer checks the voltage periodically and delivers a top-up charge, as needed.

 

The last unregulated “trickle charger” I remember seeing was at a Sears Auto department around 1990. Probably it was a clearance sale. Those humming transformers and diodes would put out 4 amps until the end of time.

Anyone buying something today will get a staged battery charger. Call it what you want, the battery won’t be damaged by it. If it’s a rusted out Craftsman bought at an estate be careful. No polarity protection either.

 

Yeah, of course, you need something smart so that the battery is not overcharged. Don't go el cheapo on it. LOL

These are my points:

• Any car battery will die if the car is not driven regularly.
  • I had a brand-new 2009 Corolla with a Japanese GS Yuasa battery (size BCI 35?) that I wasn't driving regularly. The battery bit the dust. The dealer replaced it for free under warranty with a Toyota TrueStart with no questions asked. Nevertheless, I felt bad about it because I knew it was my fault. If a lead–acid battery is kept in a low SOC for a long time, it will permanently fail.
• Hoping that some OTA software update or disconnecting the negative terminal to reset the system will fix things is wishful thinking. Gen 4 didn't even have software updates.
• We don't really have statistics on this. It could be that only 1% of owners are having this issue. And that could be because of driving habits.
• Even the owner's manual implicitly states that Gen 4/Gen 5 Prius/Prius Prime is hard on the battery by warning about the battery capacity (45 Ah minimum). Therefore, with what is happening, it is not unreasonable to assume that the failures might be the result of an extended low SOC due to driving habits, such as driving the car only to Burger King.

So, yes, we don't know, but I am more inclined to think that driving habits might be the main reason beyond failures. I doubt GS Yuasa has a quality-control problem.

As far as design problems are concerned, I think the only remedy would be a fast-charging 12-V LFP battery that could quickly charge even in ten-minute trips. To me, it looks like lead–acid batteries are unable to keep up with the high drain of Gen 4 and Gen 5, as their charging speed is limited. You can have a much higher charging speed with an LFP battery. Perhaps Gen 6 will have an LFP 12-V battery and a fast 12-V charging system.

 

You could probably consider the 2 amp setting on most chargers a "trickle" setting.

I had a car parked for the winter with a 2 amp charger on it. In the spring, the battery was totally destroyed.

 

I believe some people are discarding batteries that have become sulfated from being in a low state of charge. Some battery chargers have a "desulfate" setting, which I believe can restore a battery to proper function.

 

I don't know what it's called, but the last battery charger I purchased claimed to maintain a battery at full charge without overcharging it.

 

A man of your expertise surely did not do that evil dead.

Some modern chargers shutdown after a period of time but more often it’s a defective battery or was connected to a constant voltage source such as used in gate openers and alarm systems.

As you know, battery health is just one reason to start and move a stored car. Ask Jay Leno, perhaps a source you can trust for confirmation.