AGM Battery

I was looking at a picture of a 4th gen engine bay someone posted yesterday, and man-o-man the inclusion of the 12 volt battery has made the driver's side crowded. @Raytheeagle was bemoaning the parts removal (or shifting) required to get at the EGR, if he ever does.

It reminds me of the fridge, the day after a turkey dinner: you have to pull half the stuff out to get to what you want, lol.

 

The design specs and my personal experience AND the reports from maybe a thousand other owners......leads me to the conclusion:
Continuous charging at 14.4 volts is more LIKELY to cause a conventional battery to gas MORE than an AGM.
AGMs were made to be a direct replacement for wet cell types......and have a longer life under the same circumstances.
I think they accomplish that most of the time.

 

Hasn't he done that already? I am not likely to play inside of PRIME's engine compartment much, but I know what you mean by how stuffed they are.

Even for a larger vehicle, that's true. When I was changing the oil on our Pathfinder, trying to push the pin holding the plastic engine cover with a socket wrench, (it was very tight fit aftermarket pin), the socket came off and went down into the engine bay chasm. It did not come through onto the ground. I could not see where it ended up. There was no room to stick a hand deep enough to search for it. Oh, well, if I ever have to replace the engine, I will retrieve it then. lol

 

Even though I bemoan it, I’ll execute the job.

I’m at 13k currently and with 153 mpg, I might wait til at least 120k with the spark plugs.

But that’s another 4 years out to plan for.

 

For all the discussion of constant-voltage (“float”) charging in this thread, keep in mind that Prius and Prius Prime cars revert to that mode only in certain non-normal conditions.

 

It's certainly a more intelligent charging system than 1 fixed voltage that you find on some cars, but all it is really saying is exactly that. Even so, it doesn't give specifics. It says "This system controls the voltage in order to maintain the capacity of the auxiliary battery optimal condition when auxiliary battery capacity is high". This is exactly what you find on external "intelligent" chargers. But what is this voltage control? 5V? 100V? A range of voltages? Pulses? Etc? If its controlling the voltage to the most commonly cited voltage to "maintain" a fully charged flooded lead acid battery, just like nearly every intelligent external charger, that, is most commonly a float voltage of 14.4V, unless you specify an AGM charging scheme. There is no easy way to detect an AGM battery automatically. There is no way to tell the Prius that you've installed one. So without specific voltages being listed, or a claim by Toyota that it's designed with an AGM battery in mind, the risk is still there.

 

You keep repeating this 14.4V as a "common" float voltage and I think that is absolutely, positively WRONG.
Unless maybe you are talking about a cheap charging system that has only ONE voltage output.
Just exactly what evidence do you have that any decent charging system is designed to "float" at 14.4 Volts; that is, the charging voltage never goes below that ??

 

"Constant voltage" and "float" charging are not necessarily the same thing.

 

I feel like we're going round in circles. Who said anything about "decent" charging systems? We still don't know exactly what the Prius does. Is it decent? Is it designed for AGM batteries? (Probably not) Does it automatically switch to an AGM mode? (No). Is the charging scheme it uses safe for AGM batteries? (Don't know).

Let's be clear here... I'm not saying EVERY charger switches to float charging at 14.4V. I'm not saying they should use that voltage either; I've corrected my "should be charged at" to "often are charged at". What I'm saying is that this value is commonly cited as a voltage that car batteries are floated at, often by virtue of the fact they use one fixed voltage for everything. I've seen as high as 14.8V cited too. Numerous alternator fixed voltage regulator replacements specify 14.4V up to 14.8V as their output.

You asked for evidence... first few hits from Google...

"Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive." Absorbent Glass Mat (AGM) Battery Information - Battery University

"Traditional alternators maintain their voltage between 13.8-14.4V" Aux Battery Charging With Smart Alternators | 12 Volt Planet

"A healthy battery alternator combo should give a reading of between 13.8V and 14.4V." How to test a car battery | Haynes Publishing

"Lucas alternators put out 14.4v with their internal regulators" Alternator voltage - regulator? - Equipment - Canal World

Anyway... Let me summarise again.....

THIS (what you said).....

plus THIS.....

"AGM batteries are sensitive to overcharging. ... charge should be reduced to between 2.25 (13.5V) and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit (e.g. AGM batteries) could overcharge the battery" (Source: Absorbent Glass Mat (AGM) Battery Information - Battery University)

= BAD.

We don't know that the Prius uses for its float voltage. But we do know that AGM batteries have a lower recommended float voltage than the flooded batteries the Prius charging system was designed for. Hence, I still stand by what I said: It's a bad idea to do a direct swap without knowing the specification of the charger. Even intelligent chargers, that are designed for flooded batteries, can float above the recommended 13.5V for AGMs.

 

Butting heads with some folks often reminds me of the Tar Baby story.

Tar-Baby - Wikipedia

 

No, we are actually making some progress.

I think we now agree that 14.4 V is not a good, proper or recommended "float" voltage for any 12 V automotive battery.
Defining "float" as the charging voltage that is applied AFTER the battery is fully charged.

The fact that some/many/most vehicles might actually do that does not alter the fact that it is not best for the battery.

And you are absolutely right that you and I don't know what the "Prius" is designed to do......partly because there are a LOT of different models. I assumed that they would be designed reasonably for an AGM battery because most all of the earlier ones came with AGMs.
That assumption might not be warranted.

I think the discussion has mostly run it's course.

The quote that you posted about a "long drive potentially overcharging" and AGM battery to the point of causing some damage is just preposterous. Even the most respected sources occasionally let some bad information (opinions) sneak in by mistake.

 

Wait - Are you saying that cars that come with normal flooded should not ever be replaced with an AGM because of this? It makes senses on one hand, but on the other, I know it is done all the time and wonder how true it is. Is it one of those situations where an AGM will work, but you will not get the full intended life if you do this?

 

To confirm, the ACDelco LN1AGM battery does drop right in and work fine, correct?

 

Regardless of what is said on PriusChat, if you’re after an informed and knowledgeable answer to this question, you could check out Professor John Kelly Weber University YouTube channel. He addresses this very topic.

 

I haven’t tried one, but from the published description and photos of that battery, it would fit physically—it’s the same case size and arrangement as the original—and I imagine it would work well enough electrically, if you wanted to change to an AGM type.

As I wrote above, this isn’t something I’d usually recommend, and I don’t think we have enough information to say reliably whether the service life of an AGM battery, in a fourth-generation Prius car, would be longer or shorter than a battery of the originally-installed, “maintenance free” flooded type.

 

Even if the service life is equal, less tendency to mess up the cable clamps and mounting hardware with acidic gunk should be worth something.

 

I for one wonder how much data was used by toyota when deciding to put a flooded 12volt into the Prius when the battery was moved out of the cabin. The in cabin battery was an AGM vented?
Either way I think those whom their battery last 10 yrs or longer will praise the choice and those whom their battery doesn't last 5 years will probably replace with an AGM as long as the negative terminal is compatible with the temp sensor / all other things being equal.

 

The only "data" they needed was a lower cost for the old style conventional battery.