12V Battery

What is the source of your data?

Not what I've observed on on my volt meter that's plugged into the 12V accessory outlet.

Now you're talkin'!!

This is what I've observed. It'll start out at 14.9 and then drop down to 13.4 or 13.5. And it goes up and down as you drive.

 

That matches up pretty well with what John Kelly of Weber University said.

 

My data source right now is a multi meter that says my battery is always low, 12-12.5 unless I charge it manually where it goes to 12.7. I viewed the Weber video years ago, good it was referenced again. He says max amps should be less than 10 going into the battery, according to Toyota. His test on start went a little over 10 then tapered back. His battery was fully charged.
I am going to get a couple clamp meters, have one already on order. This should resolve my low battery problem source. It was the same on my new Prime, exactly, I had to be constantly charging to have a fully charged battery.
Rapid charging of the 12 v it does not do, as Weber shows. It powers the other demands plus the charging if needed, up to 100 amps.

 

This was discussed years ago already about 12 v charging. So how does correct info become incorrect over time? Doesn’t matter, I guess it’s humanity.
The clamp meter for dc current was about $30 for the cheapest but still looks like it has a lot of features. I have a hunch my car is fine I just don’t have it turned on enough to fully charge the 12 volt.


Toyota Prius 12V Charging System Functional Test | PriusChat

Maybe I am the one incorrect, as Kelly says the amps according to Toyota should drop to less than ten, and I noticed it was higher at first. Which the first time watching didn’t pick it up. Hopefully when I test my battery with the amp meter it will tell more.

 

Well, I wouldn't know about that, even with a search. I am new here. And Forum posts don't supersede my own knowledge of the topic.
Oh - it is the Interwebz, so it must be true.

More importantly model design and features do change over the years. One model they put a carbon-fiber hatch on, it was that important to shave some weight. SMH It is a vehicle, and there will be design compromises. It is still a marvelous design, overall!

My _impression_ of how it works is vague. I don't have the source material on how I developed that impression. I will be doing some testing, now that I am out of the 100k mi. warranty. There are some areas in which I would like to tweak the original vehicle design, to fit my own preferences on a few specific systems.

I will be reporting on those results as I progress.
If anyone on these forums have access to design documentation, please point me to them!

 

That is good to know. Saves , time, energy, and frustration. Thanks

 

Here is another video from WeberAuto. Don't worry - you don't have to replace your battery (yet), Mr. Kelly misspoke and later corrects himself.

Charge your Aux battery if it is deeply discharged prior to making [Ready] the vehicle, per Toyota.
This is in order to limit the current to 4 amps, per the battery Mfg. instructions.
That has nothing to do with the charger type.

It is a function of the mass of the battery.
My 105 A.H. Duracell AGM batteries (solar application) like a 10 ampere charge current, per Duracell.
this is 1/10 (0.1C) of the Capacity of the battery - pretty typical ratio, BUT IT IS SPECIFIED BY EACH MANUFACTURER.

4 amp limit for a 45 A.H. AGM is just right, easy to find and cheap to do. Be nice to your battery, it will live a long life.
Allow too high of a charging current for too long of a time in too warm an environment will cause thermal runaway, boiling (yes, even an AGM), venting and damage. Ask me how I know.

Oh and if you watched the video above, did you catch that the battery <charge> * charged & rested * voltage and capacity is dependent on ambient temperature.
Anybody paying attention to that?

 

What you are seeing is by design. Toyota sacrifices some battery life for a simpler system. The voltage is also dependent on ambient temperature - I don't have a chart for you. What you have observed is normal for your vehicle. That is a good bit of info - if that changes drastically, you'll know it wants some more attention

To lessen the worry, a battery doesn't need to be fully charged all the time to be healthy.
My routine is to charge several batteries (lawn tractor, power tools) once a month.

If something has been left on, or a door left open, do fully charge the 12v Aux battery before powering up [Ready] the vehicle. It will help preserve 12v battery life. Allow several hours to accomplish this.

 

This thread is a mix of Generation 3 and Generation 4 vehicles.
The O.P. was not Gen 4, the Weber video is.

There is a big difference in design.

 

And on which electrical loads are turned on, and whether the transmission is in "D" or something else, and how long it's been since the car was started, and probably other variables.

 

Yes that is all correct.

I was pointing to the battery full-charge open-circuit & rested value, independent of the car; sry for not being clear.
Yuasa says 12.8 volts for AGM, but I can't find a specification chart. They also say to recharge when the rested voltage drops below 12.4 volts. No mention of temperature.
All from their website.

 

To answer your last question, no - driving the car will never charge it to full.
An external charger is required for that, though not necessary - that drive should absolutely maintain the charge as to be useful and not fall over.

What is the specifics of the Duracell battery? - a picture of the label would be great!

 

Yes, there could be a problem with the DC/DC converter, which is located inside the inverter. Usually, you would have a trouble code if this were the case.

If you have a voltmeter or OBD2 scanner, you can use them to check. Put the car into ready mode and connect the voltmeter to the 12v battery. You should get a reading of 14+ volts. Also, see post #40 above.

Posted via the PriusChat mobile app.

 

Toyota’s acceptable range for the multimeter VDC reading on the battery is 13 to 15 V, just an FYI.

 

you said you work from home and don't drive much. that could be the whole problem

 

Maybe because they do not want to honor the warranty for the battery.

+1 for post #57.

How many times per week do you drive the car, and how long do you drive it for?

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