12V battery going dead

Exactly.

 

Here is my 12-V battery in my blue 2021 Prius Prime Limited, clearly showing the battery sensor attached to the negative terminal that measures the following seven different things: SOC, SOH, SOF, T, V, I, and self-diagnosis. It is not part of the battery. It is not part of anyone's battery. Gen 5 should have a similar sensor. The main difference between Gen 4 and Gen 5 is that Gen 5 is centrally vented so that you can plug in the exhaust hose into a side vent hole. It is the same battery and same or similar removable battery sensor otherwise.



By the way, I have never had a single issue with my 12-V battery whatsoever, including when I left my car undriven for over six weeks in hot weather with an active full Toyota Connect subscription. I never trickle-charge it.

 

I'd love to see a chronological and geographic map of Primes affected by the battery problem and also those not affected by the battery problem. I'm wondering if there's a strong correlation between Primes that were inactive for longer periods(>1 week) and that were exposed to frigid temps at the same time. Very cold weather and discharged batteries are not a good combination.

One theory early on was that Toyota received a shipment of defective batteries. What if the batteries were originally good, but a software/firmware bug caused the batteries to be depleted while the cars were in transit during the winter? That could have led to permanent damage. The batteries would have been good leaving the factory, but defective by the time they reached the owners(or shortly thereafter).

In a way, this reminds me of the 2010-11 piston ring problem. The rings weren't really defective. They were developed under the belief that 6 month/5k mile oil changes were going to be specified. But Toyota (Marketing?) decided to switch to 1y/10k mile intervals midway through the 2010 model year. So the issue was really the combination of the rings plus the longer OCI, not either one by itself.

Could we be seeing a similar situation here? The batteries were fine on their own, if a little undersized. But put that together with a software bug that effectively functioned as a mild parasitic drain, plus add some sub-zero(F) temps, and maybe we have a recipe for damaged batteries. Plus repeatedly bringing a lead acid battery to a lower state of charge and holding it there isn't great for its health either. Maybe the 470 CCA replacement battery can more easily stay in its safe zone of charge, but the 285 CCA original has too little reserve capacity and drops into the danger zone more frequently. So even if the bug has been fixed with an OTA update, the damage has still been done to many of the Prime 12V batteries.

I wonder if we'll ever know for certain. (And I'm thankful I ended up with an HEV instead of a PHEV considering where I live.)

 

I am not sure which ring problem you are talking about, but at least the Camry engine had improperly drilled oil-return holes in the pistons that clogged and caused the coking. An improper engine design can cause engine carbon deposits even with frequent oil changes. There are some oils that help clean such deposits. Valvoline recently introduced the Restore & Protect passenger-car motor oil. Previously, they had the heavy-duty diesel-engine oil Premium Blue Restore with a different base-oil formulation that contained polyol ester and alkylated naphthalene that dissolved the deposits.

I am pretty sure that it is also an owner-maintenance issue on the 12-V battery: short trips only, leaving the charger plugged in for longer than overnight, third-party accessories, sitting in the car with the lights on not in the READY mode, using the ACC mode, etc. may all result in dead 12-V batteries.

 

The low tension piston rings in the 2010-11 Priuses were a little too low tension. As the sludge builds up in the ring grooves, the overly low tension rings don't have enough spring power to stay tight to the cylinder walls. This causes excess oil to be left on the cylinder walls, which then is burned during the combustion cycle causing excess carbon to go through the EGR system. Over time, the sludging eventually locks the rings off center, which causes scoring of the cylinder walls. When this happens, you now have significant amounts of oil being burnt, which eventually causes premature failure of the catalytic converter. It also makes it far more likely to run the engine out of oil, causing spun bearings, thrown rods, etc. Keep the rings free with a combination of a shortened OCI, plus a strong oil detergent every several years, and you stop the cascade of failures before it ever happens.

As for the battery problems being an owner maintenance issue, I'm not buying it. Even with our limited sample size, there are too many users who are having battery failures that are not doing any of the things you list. There's just not a strong enough correlation there for that to be the primary issue. Something else is going on, and it's specific to the Prime. The HEV uses the exact same battery, has been sold in far greater numbers, but we're not hearing about any cases of 12V battery failures there that aren't linked to admitted user error.

 

Oh, don't underestimate/overestimate people.

It is not sludge. Sludge is the gel-like material that could happen because of infrequent oil changes. Toyota now uses boron dispersants in TGMO to disperse sludge and help alleviate potential problems.

It is carbon deposits, which happens from burning of the base oil or plastic viscosity-index improvers. It could contain inorganic additives, too. There are high-quality synthetics that help reduce carbon deposits. I believe TGMO uses polyol ester, which has high solvency, in the base oil to help dissolve them. As I said, the new Valvoline Restore & Protect engine oil specifically targets such carbon deposits. It does not come in SAE 0W-16 though.

With today's high-quality synthetics, there is no need for 5,000-mile oil changes. In fact, they have extended-performance oils that can do 20,000 miles. That said, I do it every 5,000 miles because I purchase a $50 oil change & tire rotation & multipoint inspection deal at the Toyota dealer; so, I include it with my 5,000-mile tire rotations. If I only do the tire rotation, it is actually more expensive. Of course, they try to include other services like PHEV battery fan filter cleaning for $400, which is a very simple owner-doable job that takes only ten minutes not even requiring tools; so, I kindly decline them.

 

Not sure how a shorter oil change spec would help. My take: Toyota was trying any and all tricks to eke out mpg crumbs, went with a lower friction (due to less outward springiness) piston rings. Took them till partway through model year 2014, and a lot of run away oil burning, to revise the rings. Too late for the majority of owners, with a 60k mile cap on warranty replacement.

 

does that mean the egr circuit does not need to be cleaned on cars with the newer version of rings?

 

That's been proposed here, but I doubt it. If the car's not burning oil, it'd be a fair assumption the rate carbon accumulation would be less. I wouldn't count on it being "much" less.

 

Ask if they can check and report on the quiescent amperage draw.

 

Back in the Toyota sludge days, the problem was a combination of lower-quality oil and long OCIs. (Do you know that acronym? ). Regarding piston carbon deposits, shorter OCIs probably won't help much as long as you stay within the oil's capabilities in that the antioxidants are not fully depleted and oil oxidation does not go berzerk. These days, high-quality synthetics easily do 10,000 miles, and there are high-antioxidant-content oils that can do 15,000–20,000 miles.

Sludge control has been improved, too, by using better dispersants. Toyota is keen on boron dispersants in TGMO (another acronym for you).

 

There is a snowball's chance in hell that he has a good battery. He is finally doing what everyone has told him from the beginning—have dealer fix it under warranty.

Now, he also keeps relentlessly repeating his newest outrageous falsehood that the OEM battery has a built-in battery sensor, despite having been told by several posters that this is not the case. It does not. It is a plain battery. The battery sensor is a separate component that costs $800, which you don't replace when you replace the battery.

 

There are new members here that play a game of “how mad can I make someone” on forums for fun. Sometimes they even get the moderator to bite.

 

Technicalities aside, cutting somone down, and especially talking about present company in the third-person tense, is never progress.