12V dies every two years

Charging voltage and open-circuit voltage are two different things. Open-circuit voltage is measured with the charger disconnected and nothing connected to the battery except the voltmeter, which is the battery under no load or no current flowing through it, as otherwise the voltage drop across the internal resistance of the battery contributes to the battery voltage due to the current flowing through this internal resistance. A very small current shouldn't affect the results much. When we are talking about the battery state of charge (SOC) for a 12-V battery, 12.8 V for 100% SOC refers to an open-circuit voltage of 12.8 V.

 

With the Victron charger, the only separate battery selection is for Lithium-ion batteries. As I stated, the charger allows custom settings, but the manufacturer recommends no such change is necessary for most common types of battery including flooded lead acid, AGM, and Gel. Thus I never bothered to change it from the default "Normal" setting.



On the other hand, my other much cheaper Chinese "smart" charger by Suaoki had three battery-type selections. SLA, AGM, and LiON. But this charger was not programmable. I had no way to change the preset voltage. And the manual was poorly written, such that I did not know what voltage settings were preset. I did not trust it, thus upgrading to the Victron.

In my use case, the fob is almost always within the range. The car is usually parked right next to the house and the key is usually placed close enough to the wall such that it can open, lock or start the remote climate in the car from there. Still, turning off the SKS, either by the fob or on the car, had no appreciable effect on the 12v battery drain on my PP's 12v battery.

 

I have established the basic facts before. The battery monitor I have connected to the 12v battery draws minimal current while connected ~1.5mA such that by itself, it does not change the rate of a normal drain on the 12v battery appreciably. And, as I have said, I only charge the battery if the battery resting voltage drops below 12.3v and I plan not to drive the car for a while.

As for the overcharging issue, if you connect a 12v battery to any "advanced" or "non-advanced" battery charger, and measure the voltage at the battery terminal shortly after the charger is disconnected. It will likely show over 12.8v. If the use of an external battery charger/tender causes immediate destruction to the 12v battery in a few short hours, then I think there would be no battery chargers sold on the market today.

 

What cars, battery tenders, or smart chargers are overcharging the battery?

That is the range the fob has when putting out an active signal. It isn't the range of the SKS. Otherwise, someone could unlock your car, and start it, with the fob 100 plus feet away.

My understanding of the SKS is that it is the car that puts out the active signal, not the fob. It does this when someone touches the door handle, or even when movement is detected. A short range ping is put out to see if there is a fob nearby. If so, the fob responds, and they connect. If not, the SKS goes back to low power standby.

With older models, the pinging from the car can be a power drain because the components weren't the most efficient. Every person or car or even critter passing by would trigger a ping from the car. Parked in a place with a lot of traffic, it can drain the battery.

The system is more efficient with newer models. For it to be a drain on the 12V, something needs to cause the car to ping for the fob, and the fob needs to be close enough to respond. The draining then comes from the system in the car remaining awake for extended periods, waiting for a fob holder to do something..

 

OK, I understand that for someone who keeps the fob within a few feet away from the car all the time, yes, the SKS may cause an excessive drain on the 12v battery. But even if that is the case, for my use case, the fob is not close enough to keep the car awake. So, the SKS alone can not be the major culprit for the "normal" 12v battery drain on my PP. And the point I was trying to make in my observation is that no matter how SKS works, I have shown on my PP with my fob use, either with the fob off or the car's SKS off, the 12v battery still drains.

 

No charger is smarter than Toyota's built-in 12-V charger, as the latter uses a battery sensor that measures the current, voltage, battery temperature, SOC (battery charging percentage), SOH (battery degradation percentage), SOF (starting performance), and self-diagnosis result. It also operates on Toyota's conservative specs. An aftermarket smart charger will measure the voltage and current at most. It looks like your aftermarket charger is overcharging by 0.2 V, which is probably not a big deal but not ideal in extending the battery life either. If you could program it using the app, perhaps you can set the maximum open-circuit voltage to 12.8 V or perhaps reduce the cutoff current or something to achieve that in effect.

 

Well, I get you don't want anyone to use an external charger to charge the 12v battery and you wholeheartedly believe in Toyota engineering to be perfect and never making mistakes. I am fine with you not using an external charger and keep saying there is no problem with a PP's charging system. I have not had a reason to doubt that yet on my cars, but I have read plenty of people with a PP or Gen4 who had problem with the OEM 12v battery premature demiss. Tell the OP of this thread to keep driving his car and do nothing, and see if that fixes the problem.

If keeping the battery SoC below 12.3v is bad and charging it above 12.8v is equally bad, then I guess, doing nothig is probabbly the easiest solution for most of us. But I am not convinced that is the solution. Although I am not likely to keep my car long enough to be needing to replace the 12v battery, I will keep doing what i have been doing for the rest of my ownership of this car. If I experience the early death of the 12v battery, then I will report it. At least that would add one data point indicating that charging the 12v battery using an external battery charger does not prevent the premature death. So far, I have not read a single case report in which someone reporting the car battery died prematually because (or albait?) he/she was proactive monitoring the battery and charged it using an external charger whenever the battery resting voltage got lower than 12.3v.

 

This thread is not the first report of early 12V battery death in a Toyota hybrid.

 

More than a decade ago, my brand-new-non-hybrid Corolla 12-V OEM battery died because I wasn't driving the car frequently. It was replaced for free under warranty with a Toyota TrueStart battery. Prius Prime has better 12-V battery management than most cars, as I said, a 12-V-battery sensor and computer being on board.

 

The charging system in the Prime will get the 12V to its ideal charge voltage, assuming an aftermarket battery is of the same specs as the charger was designed for. Then when parked on a warm day, the ambient temperatures will warm up that battery, bringing the effective charge above ideal.

Underlined the important part. This isn't a warning about getting a 12V 0.2 volts over its ideal 100% charge voltage. It is about hooking the battery up to a manual charger, and then forgetting about it. Putting 13.8+ volts into a battery for the entire charge session, and continuing to do so after it reaches 100% SOC can be very bad. A couple other bullet points they left off were possible fire and explosion.

No one on this thread is doing that, nor recommending to do so. Also haven't seen anyone recommend a manual charger over a smart one here either.

 

If a battery is specified for a specific Full SOC by the manufacturer and your charger thinks it needs to be higher then your “smart charger” is going to be pushing a higher charge, boiling the acid (effectively giving it an equalization charge) each time you use it. You will be adding water, reducing the specific gravity, charging the battery more often (because your “smart charger” will be trying to maintain a higher Full SOC). End result: significantly reduced battery life.
Perhaps that is one of the reasons we keep reading about how short of life Prius aux batteries have. ie: owners ignorance?

 

You are dead on point.

@Salamander_King's post shows that turning the car on for less than one-hour-a-week is sufficient to keep the 12-V battery fully charged.

Why would you need an external 12-V charger with a PHEV? If you are not going to drive the car, make sure that you have about 40% SOC in the EV battery (higher or lower SOC will degrade the EV battery), and all you need to do is to turn on the car to READY mode and keep it on for one hour a week, which will fully charge the battery to Toyota specs every week. If the 12-V battery is fully charged, it will easily last for two months without being charged or the car being turned on.

It is also ridiculous that people are worried about the 12-V-battery life but totally ignoring the EV-battery life. Many people never charge the EV battery, which is really bad for it and can cause a failure within a few years. 0% SOC is not the correct long-term SOC maintenance point for the Prius Prime's EV battery.

 

i keep a semi-smart charger on my 17 year old dakota battery

 

Boiling off water, then replacing it with a like amount won't change the specific gravity.

The warning for over charging includes a part about killing the battery in hours. That doesn't happen with a slightly elevated voltage reading. Which we are assuming is correct, and not just the meter displaying high. The poster who had such a reading isn't having having early battery death.

The OP that is, and many of the other reported early deaths in Toyota hybrids, are just relying on the car for charging.

 

I’m sorry, but without the subsequent recharge, adding water does in fact dilute the battery acid, thereby reducing specific gravity. Pure water added to any liquid reduces the liquid’s specific gravity. One of the basic laws of chemistry and fluids.
The OP was asking if there was a problem with the vehicle, which there is if the vehicle is destroying batteries as the OP indicated.

 

The fact that any of us does something doesn’t make that action correct.
Besides, the charging system on a 17 year old Dodge Dakota is definitely not controlled by a system anywhere near as sophisticated as the one in a Gen 4 Prius.

 

i didn't say whether it was correct or not, just that i do it, and i'll add that it seems to work well. but it's not a scientific experiment, just observation

 

I charged a bank of 12 vdc solar batteries at 15.5 volts using a very smart charging system, but it is NOT something I would do on a Prius.

 

The boiling point of sulfuric acid is 337C. Unless the charge session has gone really wrong, the acid isn't being boiled away, just the water. Now, adding water to a battery that isn't fully charged could result in dilution of the acid, but since the discussion was about overcharged batteries, that probably isn't an issue.

 

“Boiling” in this context isn’t actually what is happening. The term is commonly used for the chemical reaction that is occurring in each cell when an external charge is applied to the battery. When the charge is applied correctly off gassing occurs and those gases are released from solution (thus the warnings concerning charging in the vehicle and charger manuals). When too high of a charge is applied this off gassing is amplified, along with damage to the plates, reducing the battery’s ability to maintain the charge and increasing the drop in voltage. Subsequent charging causes excessive off gassing and the cycle continues. Thus the battery can no longer operate as designed.
Different manufacturers use various plate thicknesses and materials. Thus different charge rates and recommended voltage levels. Each battery has a certain number of charge cycles (life expectancy), even if they are a “full charge cycle”. When a battery is recharged more frequently than the design basis, and unnecessarily, cycles are used up and the battery doesn’t last as long as we expect.