OK 57 Chevythunder, I received your summary. Very comprehensive. I certainly appreciate all the info you assembled and to take the time and effort to get it posted and shared. The dealer decided to give me a new battery. I'll post later as a followup.

 

You are certainly welcome. It only seemed right to try to get this information out to as many people as possible.

Happy for you that your dealer is replacing your battery. I really do think there will be a lot of people that will be replacing batteries earlier than in years past. -at least in those cases where the fuel economy mode runs their system voltage down to 12.5 and keeps it there for extended periods of time, like mine has been doing.

Maybe the answer will be to just run with the headlights on during those times when the system switches to the fuel economy mode, thus forcing it into a safer voltage range.

And certainly in my case, I will have it connected to the battery tender every time it is parked in the garage. (-which in our case will be a lot of the time).

I think the bottom line is that "time will tell" just how it all works out. But at least now, we can all know how these new charging systems work, and why they work that way. (-whether we like it or not,,,)

Here is wishing us all good luck on our new cars.
In my very definite opinion, the design is truly fantastic, and hopefully over all "they got everything right." One thing for sure, the public acceptance on this generation of Impala has been huge. -for example, just look at Consumer Reports review on the 2015 cars, and see how the new ones compare to the Impalas of past years. WOW, night and day differences.

We REALLY LIKE ours.

 

Okay Guys and Gals, here is my latest ONE PAGE document, attached below.

I think it will be a much better document to share with others. It does not contain my personal biased feeling on the subject, etc., but rather just sticks to the facts.

Again, thanks to everyone on this thread, and on this forum who gave me the impetus to thoroughly research the subject, and spend the time to write up the summary.

"Stay in touch!"
And enjoy your new Impala.

 

The Rookie is still at it. After my dealerships service dept ran a computer analysis on my battery (48PS) two times, each time indicated ok, I asked for a new battery for testing. They agreed. New battery conformed exactly as described in Thunders description which conformed to GM's specs. I now start the Impala and DIC displays @14.5 Volts for @30 seconds. It then drops to @12.6 Volts for the duration of my trip. What a thread and forum.
Thanks again Thunder and all others for your participation. Have a good day.

 

you must buy a lot of cars for a dealership to spend the time to do that.

 

Hey I say "stick with it" until you feel like you have the right answers! And as Tech2's reply indicates, it certainly appears that you have a very good dealer service department that really wants to do what they can to have a satisfied customer. I'd say you are fortunate. (-of course sometimes it is a tricky balancing act to not "wear out one's welcome.")

So Rookie, I have to ask you: In your opinion how do you think this new charging system is going to work out for us all in the long run?
Man I'm still apprehensive. But once again, I sincerely hope the engineers actually did "get it right."

Honestly probably a large part of my problem is I am too old. I have been a "gauge watcher" all of my life, and the old norm of 14.x volts during normal running just isn't the way it is any more. My apprehension still centers around the "engineering decision" that an 80% State of Charge on the battery is adequate. -hence the Economy Mode kicks in.

Man, I'd really like to have a detailed conversation with some battery engineers, -or maybe even battery tender engineers and see what their position is on this 80% state of charge being okay.

I guess the bottom line for me is that "time will tell." And one thing for darn sure, the battery tender cable will be plugged in every time it is parked in the garage.

Rookie, thanks so much for your reply to let us know that yours is acting just like mine, with your 12.6 reading. (mine is always 12.5, which according to the GM tech service data is also dependent on the "computed battery temperature") They sure do prefer to run in that Economy Mode.

Now, to play devil's advocate for just a moment, my good old 2002 Bonneville with its "low tech" 3800 consistently gets around 28mpg on the highway. So the highway mpg's on our new "high feature" 3.6's kind of makes me wonder,,, -and honestly these new 3.6's probably will do better mpgs in town I suppose. -seems to me the Fed's fuel mileage law has got them scrambling for every hundredth they can get out of them.

---Just saying,,,,

Otherwise, we are totally loving this new Impala design !! -hope you are too.

 

I miss the oil pressure gauges.

My last j-body didn't have volts or oil pressure.

 

Man I'm with you 100% on that one too.

 

where does it say that?
12.6 volts is fully charged battery. pretty much every mode will maintain that.

 

Tech2, Yes, 12.6 would be better than my 12.5 readings. (in fact with lead/acid, 12.66 is "open terminal voltage", fully charged, depending on temperature of course) -I would be super happy with a reading of 13.

Okay, with the question being, where does the "80 % state of charge" come in to play in the "Fuel Economy Mode?"
I have no idea what access you may have to GM Technical Bulletins, but with your username of "tech2" I'm hoping you can maybe directly access the official GM source?? (just as an ordinary vehicle owner, I certainly have no way to do that. So I paid a visit to my old time acquaintance/shop foreman at my favorite GM dealership service dept, and he logged in to his account, and pulled up the bulletin specific to my 2015 Impala.) -I think the chain went like this: "2015 Chevrolet Impala/Impala Service Manual 7525949/Engine/Propulsion/12V Starting and Charging/Description and Operation/Document ID 2809645"

And having carefully read through that five page bulletin on his computer screen, I can say for sure that the AGCO article is essentially the same, just nicely summarized.
That AGCO link is: AGCO Automotive Repair Service - Baton Rouge, LA - Detailed Auto Topics - Why GM Voltmeters Show Low Voltage

-from the AGCO site: "A calculated state of charge of 80% or more and ambient temperature above freezing sets fuel economy mode. The voltmeter will read as open battery voltage in this mode. A reading of 12.5 to 13.1 volts is normal in the fuel economy mode."

-from the GM bulletin: "The BCM will enter the Fuel Economy Mode when the estimated battery temperature is at least 32 degrees F but less than 176 degrees F, the calculated battery current is less than 15 amps and greater than -8 amps, the battery state of charge is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5 - 13.1 V...."

So there it is, and my Impala is running at exactly 12.5 when in that mode. (verified with DVM at power point connector).

Hope that helps !!
-And hopefully you can get access to the bulletin to read it in person. It sure was an eye opener for me!!

I have also verified the 12.5 volt/80% figure via a couple of "battery state of charge" tables (readily available from several sources.)

And once again, I fully appreciate you and the others on this forum who have been good at "digging out the actual facts."