The electrical charging system is truly weird from what I have been used to. After discussions I've followed on this forum, I finally started paying attention to the "running" battery voltage as I drive. I had the GM charger on overnight to ensure a full charge and then went for a 45 minute cruise or so. I didn't look at the battery voltage for the first 10 minutes (took a while to relearn/remember changing dash - I was driving so I was focusing on that). But once I had the battery voltage displayed, it was always reading 12.5, occasionally 12.6. I assume the C8 drops the voltage 0.2-0.3 from 12.8 (fully charged) to power running loads, so the alternator was never given the command to turn on and start charging.

I know that the alternator is ok because I have seen 14.2-14.4 occasionally displayed (on my radar detector) prior to today. I'll be paying more attention to it now, but it appears that the battery is constantly being drained without charging for extended periods unlike the old days of keeping a running voltage of 13.x to 14.x As some have posted, GM and others are doing everything possible to raise the mileage for the EPA requirements. Hard to believe that running an alternator in a car makes that much difference overall. Especially when the energy extracted is not linear. The efficiency drops as output increases. Multiple lower charge rates/cycles (float & acceptance) would be better than an extended off period, then high (bulk) output to recharge all the way back.

It will take many more drives and data collection to see what is actually going on. I'll skip the charger and drive again soon and observe the voltage. It would be interesting if others do similar data collection.

 

Quite honestly, it's a waste of your time. My last late model GM was exactly the same way, to the point I took it by the dealer and they confirmed that's the way things are now. I lost a battery at about 60k miles and it was only a few years old. They said, yeah it's not uncommon for a battery to go bad that early. I didn't fully believe them, but without changing any parts on the charging system the next battery took it to 180k miles and was still strong when I got rid of the car.

 

Actually, from research I have seen, "smart" alternators improve fuel economy around 1%.

 

1% would be apx 0.2 mpg. Possible, but I would think it should be lower assuming battery is in good shape requiring less of a constant charge.

AC on the other hand can make a big difference. 2-5KW (5-14hp @50% efficiency) Many offsets here though. Insulation vs weight. Tinted windows,... Not desiring to go off topic though - just another example of scale. Alternator average minimal output @ apx 30 Amps = apx 0.4-0.8 hp.

My biggest concern is how the lower running voltage affects all of the electronics on board. Someone mentioned that there are apx 165 or so PCBs on the average vehicle. And from personal experience, voltage below 12.5 can be significant on some (not all) electronic operation. Something else to live and deal with.

 

After not driving for a couple of days and not being put on the battery tender I saw 14.8 for about 8
miles or so, then it dropped down to about 12.8. This is exactly what I would have expected.

 

Yep, the world has changed! Could quote a page from my 2014 C7 4 Volume, several thousand page Service Manual BUT I'll provide a simpler explanation! There is no longer an electrotechnical or solid state voltage charging system. A computer, like most things in the car, is controlling charging. Since my early 2014 C7 this question has up on the forum many times. Yep once at about 12.5 the alternator is not doing any overvoltage charging, which is all the old systems were doing. Not needed and wastes a small amount of energy. Actually about all new cars operate the same way.

SIDEBAR
Perhaps what my wife's BMW X5 SUV does will give perspective where the World is going re saving energy (and significantly reducing CO2 emissions.) Her car has Stop/Start and it's so non intrusive I never turn it off. It also ONLY turns on the alternator when braking! Has a meter showing when it is recovering braking (and coasting) energy. It has two batteries, a large AMG battery and a smaller one. I have driven in cruise control for a few hours and seldom saw the alternator connected! But since start/stop requires an electric water pump and other "stuff" it does use more battery power when stopped. Hers will be 3 years old and no issues. Frankly I see where the C8 looks like it's being prepared for Start/Stop. May only be used when the hybrid C8 is introduced. Yep we're in a New World- like it or not!

Replaced my September 2013 built 2014 C7 battery at 2 1/2 years with an AGM since the battery voltage was reading low (after 24 hours to let the surface charge dissipate.) Hardly every used my battery charger. Probably a weak cell from the beginning as it was always somewhat low.

Now my street rod with a conventional old charging system is on a maintenance battery charger 24/7 (unless at a car show.) Recently replaced it's Yellow Top Optima AMG battery after ~8 years JUST as a precaution! Yep IF you're worried about battery life a charger helps. I don't care as batteries are cheap and hooking up a charger is a PIA. I have been on vacation ~3 weeks most of the 7 summers I had C7s and never used a charger. Too much chance of lightening storms in the summer. I can rewire the street rod since I made the diagrams and did all the wiring from scratch myself. Would not want to every have a dealer tech do that with a new Vette! Have replaced the sprinkler controller in the house twice from lightening!

 

As one deeply involved on a professional level with batteries and charging, I'm amazed that no one (at least I haven't found one yet) has yet to create a proper charging system. Bottom line, once charging is 100 % complete, it needs to turn 100% off and then a programmable setting should kick in on when it needs to turn back on to check if charging is necessary or turn back off again for the setting level. Of course minimal electrical drain is required to keep the device on. Btw, this device could be a separate (external) PCB or included as part of the charging system. Constant or overcharging is the #1 reason for premature battery failure - reduction in battery lifetime.

With the typical car battery in the $100-200 price range, it may be moot, but many other situations require battery banks costing thousands to tens of thousands of dollars. And they are routinely killed prior to what is possible for their lifespan.

 

^^^
That appears to be essentially what the computer controlled C7 and C8 car charging systems do. May not be exactly what you are referring to but appears close.

In addition the GM labeled external CTEK Swedish charging system operates about that way as does my less expensive Schumacher (yep same drag racer who has several AA/Fuel Dragsters and Funny cars in his racing stable) has done for 20 years for my Street Rod that operates 24/7 when it's not at a car show.

Seldom use the equivalent to the GM CTEK system I have (bought in 2013 from Amazon - at that time about 1/2 the GM cost.) Mine is a DD and I don't bother connecting even when on several weeks vacation. When a new battery is needed I'll replace with an AGM.

Bought the Schumacher charger 20 years ago. Recently replaced the Street Rod Yellow Top Optima Battery after 8+ years. It was actually operating fine BUT the battery is inside the sedan and I have electric remote operated doors. If it failed at a Show would be a PIA (I do have a way to get power to driver door solenoid IF the battery or remote control failed, if I have it home BUT a PIA at a show!)

Yep a quality battery charger that monitors voltage and only charges when needed will extend life. The Schumacher charger does keep it at a somewhat higher voltage than needed but 8+ years battery life is enough for me!

 

Again, I'd have to check, but no charger (i have looked at) turns completely off. They all go into a float mode apx 13.2 Vdc at minimal amps, but that is still on and charging. The scenario with the C8 is somewhat there, but less than ideal for the battery itself.

The simplified analogy I use is once a balloon is 100% full, putting only 1 more breath of air in will cause it to blow, no matter how little or slowly performed.

I thought about manufacturing one (external regulator) once upon a time, but people are ... and commitments prevent further development.

 

^^^^
CTEK sells a number of types but all operate about the same way, some with more "steps." They also brand label for GM, Ferrari and many other manufacturers. Most like GM have fewer buttons and control options.

Pic is two common models:

 

Like I said, I have yet to find one that is designed "properly". Any absorption voltage (beyond the 14.2-14.4 for a 12 VDC battery bank) absolutely kills AGM batteries because they are sealed. Not good for wet cells, but the water can at least be replaced that was evaporated. Absorption is strictly a manual vs automatic operation and again just for compromised wet cell batteries that have been sulfates. Step 7 needs to be float voltage 12.8-13.2 (depending on cell makeup) and zero amps once 100% charged. Float is sort of an oxymoron. Once 100% charge is completed after the absorption cycle, the charger should turn off. If in "float" mode regardless of the voltage above or at fully charged state, if the amps are above zero without any load applied, you are overcharging the batteries. Just like keep pumping gas after the tank is full.

Float mode was designed for those too lazy to monitor and turn it off. One could say a similar thing about automatic transmissions (except the C8 of course - lol), but not exactly as automatic transmissions actually have a purpose.

I get questions all the time on this subject and I ask them, does your car tell you when to get gas? No, it is up to the driver depending on many inputs to the situation. Battery charging is the same. The alternator charging in cars like the C8 are a step in that direction, but due to epa ramifications are overriding what is best for the battery itself in the long run.

 

^^^
Perhaps the less expensive Schumacher charger works so well on the spiral wound cell Optima Yellow Top battery is it does inherently have a somewhat higher voltage. Fewer connections versus plates connected in parallel.

As I mentioned, I only replaced it after 8 to 9 years because I was concerned it had been in the car so long! The battery is in the right rear interior of the 2 door sedan that uses a remote control to activate the door solenoids and front windows. If the battery fails (or the remote control) can't get in the car! I have a way I designed to get power to one solenoid and if it were in the garage could manage to supply power to one door. BUT would be difficult if at a car show.

Since I fabricated a battery hold down that fit the round cells I just bought an exact replacement. After that long time it was cracking that high compression 8.2 Liter BB with no trouble!

 

The "charging system" in a car doesn't just charge the battery, it powers all the electronics in the car while the car is running. If you shut the charging off completely, the battery would drain rapidly. Modern charging system work correctly, feeding the battery just as much current as is needed to keep the electronics active, the car running, and the battery not draining.

Allowing the battery to discharge, then turning the alternator back "on" to charge it would reduce battery life, not improve it.

 

And I'd like to add that in a performance setting during WOT a system voltage closer to the batteries is desirable because the capacitance of a large battery is stabilizing feature for automotive signals (It will reduce electrical noise and risk when alternator is charging near battery voltage 12.5-12.8v Instead of high voltage 14v)

In other words, automotive sensors and triggers work great at 12.5v and the modern computer controlled alternator can be programmed to target 12.5v to 12.8v ranges at WOT to minimize noise of the electrical system and prevent fluctuations.

To put this one more way: When I tune a daily driver turbocharged 800rwhp V8 on alcohol, using an aftermarket alternator with a stand-alone, I Set the target system voltage for WOT near 12.6Volts for a variety of reasons:
1. reduce electrical noise from AC generator alternating current supply source
2. stabilize system voltage using battery capacitance
3. eliminate potential issues with alternator failure, alternator cut-out, alternator short supply, etc...

Alternators are not all *good*. Some produce noise, or wavy output signals. An alternator can also go bad. It is a wear-item for the engine.
Therefore, tuning should NEVER be done using the alternator output as if it were a dependable source (never tune an engine solely at 14v, always perform 12v tuning regardless). In some vehicles there is no choice but in many modern vehicles and typical modern stand-alones there is a duty cycle controller for the alternator voltage specifically for this reason.

At WOT if the alternator fails, belt jumps, or suddenly provides a poor signal, If the system was being held at 12.5V already then there will be no detrimental effect to the engine.
However if at WOT and the alt fails and the system was running at 14V, suddenly the voltage will drop to battery voltage. The sudden change in voltage will affect many systems, injector quantity of fuel injected for example. Which is not something you want wavering or changing at WOT- ever.

 

My friend that races uses a 16Vdc battery and no alternator.

My best guess to the various Frunk and trunk issues that were not user error are related to the electrical system somehow. Not sure where or which, but it is there somewhere. And due to the random, unrepeatable nature, my hunch is it's in the charging system PCBs or the alternator itself and how they react during the initial startup as voltage and draw varies. But that has been a circular subject. No need to redo.

 

As has already been suggested, apart from newer charging systems acting differently than many expect, current battery quality is highly variable and unpredictable... unfortunately.

 

I revisited my Battery Condition during my Lift reinvestigation.

FYI, battery has an embossed date code in DD/MM/YY format (for those not use to seeing it that way. Maybe made in Canada?)

As I left the battery on the charger overnight, I wanted to check the voltage and it did return to 12.83Vdc that it never seems to have when my C8 is running. The reason for my investigation is being that the battery runs at 12.5 Vdc most of the time, I was attempting to investigate the battery water level (which could cause the lower volatage too), but even me (in the business) am unsure if the battery is a standard wet cell or an AGM. If the latter, the last thing I would want to do is force the 2 caps above the cells off. If anyone can confirm (100%) that the battery is either Wet or an AGM, please advise. I have seen these type of caps on both versions.

 

^^^
I'm 99% confident the battery pictured above is a flooded wet cell. It looks just like the battery in my C7 that I replaced with an AGM battery.
And I've never seen an automotive AGM battery with removable cell covers.

 

I probably agree. I went to the ACDELCO website and found the battery. The others listed on store websites have different (close) CCA numbers.

Part Number: 48PG
Product Notes:
42 Month Warranty
All; BCI 48, minimum vehicle Reqment: CCA 730/RC 120; OE replacement
Per Vehicle: 1; Years: 2020-2021



But as I dug a little deeper, I found the following - Apparently, these new maintenance free (Wet) should not be opened either.

What is the difference between a (Accessible) Maintenance-Free Battery and a Filler Cap Battery?
Batteries that are Accessible Maintenance Free or Sealed Maintenance Free have a Calcium Additive to the plate material inside the battery that helps to prevent the gassing off of electrolyte. These types of batteries should never need to have water added. Vent caps on these batteries should not be removed at any time as this breaks the seal and could allow seepage or water loss. Low electrolyte in these batteries is an indication of overcharging. Filler Cap batteries have an additive in them that requires the checking and refilling of the battery with distilled water.


I don't expect the C8 will ever overcharge so there will not be a need to check.
So good thing that I did not open it after all, even being a "wet" cell type.


So the only item under the covers not "readily" accessible for maintenance investigation is the front lift reservoir. The battery will only need access for a jump or replacement.

 

When I fully charge a new battery I generally see 13.5 - 14v or near that when I pull off the charger "surface charged".
After a minute it will drop around 13.35v without the charger dis-connected
After 24 hours I still see 13.05v

I get this same result with a regular car battery (new from walmart) and with a compact, sealed lead acid (mighty max).
The point being many chargers won't push a battery "to fully charged" this includes many cars' alternators. I am not sure why. Most cars will only put a 12.8v charge on a battery. Maybe they are purposefully limited to keep from overcharging. However if you leave a battery at 12.5 or 12.6 or 12.7 all the time it will more quickly deteriorate I believe so I constantly top my battery off when I get the chance.