This has been beat to death with many opinions. I don't need or want to go there.

This morning (always on charger, cool 65) when i took my Game Changer out for a spin and tge battery voltage was a surprising 14.9 Vdc. Previously, I have never seen it above 14.2 and then for a very short minute or so before it started to drop back to 13s then 12.5. It stayed at 14.9 for a minimum of 20-25 minutes stop and go and short highway driving until I came to a stop light. It then dropped to tge usual 12.5 and has stayed there (SOP).

My battery is still the OEM from July 2020 delivery. Any chance it's giving me a warning to replace soon?

Any ideas why this out of the blue?

 

Update

Went into store for some shopping, out 30 minutes later, started 14.3 for 30 seconds then 12.5 - back to normal charging cycle.

Stopped by my dealership and spoke to my technician. No real explanation available.

 

I''m no expert, but if it's charging over a certain (I don't know say 11.5 volts just to make something up. Somebody else will weigh in with more accuracy) then the battery is OK. To me, I try to remember the old adage, "Use it up, wear it out, make it do or do without".... So I don't "preventively replace batteries. If they begin to fail in their ability to start the car, that's a different issue (for me)

YMMV

My 2¢

 

That's always been my philosophy, but with the nature of this animal, I don't want to be out and about and deal with it then. I just reviewed hiw to get in with a dead battery. Lol.

 

My brand new C8 and battery ran 15.4v most of the time for the first 500 miles even during an hour highway drive or after it had been on a tender for several days and the battery was FULLY charged. At about 900 miles it started running somewhere between 12.5v and 14.5v like would be expected with this wonderful "Green" charging algorithm. I worried that the system was defective and would constantly over charge. Nope it has finally embraced the rules it was ordered to live by. I'd say yours is operating just like it's supposed to and your battery is still good. Load test it if you are worried.

 

ugh… props to you and I thought I was ****

 

As I mentioned in my first post, I do not want to get into battery charging wars. I was concerned with the 14.9, but everything is back to "normal" after a 20-25 minute drive.

?? What was happening between 500-900?

I am an "expert" in the field. 15.4 is in NO WAY OK or normal. That is used for/during equalization of a sulfated battery. During equalization, the batteries will bubble and emit gas. With sealed AGM batteries, this will boil out the little fluid in the absorb mats and kill the battery if it is not already. A very short accidental exposure would probably not kill a battery, but many hours at that voltage does in fact degrade a lead acid (Wet Cell, AGM, ...) if it is performed on a good 100% sealed type (AGM) battery in a new condition. Every single AGM I have ever done an Equalization cycle on has 100% been destroyed. They were bad or dead to start with, so no loss there. Wet cells are able to have the distilled water loss replaced and doing an equalization may work at times.

Chevy/GM is holding the charging algorithm secret so we will never know what is actually occurring or why. Sad state like the SS I created in 2020 to explain at the time an idea of expected manufacturing / delivery dates.

Below is a normal charging cycle for Wet or AGM batteries.

 

A fully charged battery left idle for an hour should read 12.5-12.7 V
A fully charged battery (before) left on a (plug in) charger for an hour (after) should read 14.2 V and no higher.

Higher than 14.2 V (for more than a few seconds) is indicative that a cell in the battery is beginning to get resistive OR that the charging system is not reading a fully charged battery (could be due to where the battery V is measured {likely at the alternator}).

 

Again, some always want to disagree and ... read the graph. It's from the leading AGM battery manufacturer in the world.

A good manufacturer uses 2.2 Vdc cells. In what is called a 12 volt battery actually has 6 of them wired internally in series for a total 13.2 Vdc when 100% charged. Less desirable low cost use 2.1 cells yielding 12.6, some in the middle yielding 12.85. This leads to many misconceptions and untruthful information. A properly manufactured Wet Cell or AGM battery is in fact 13.2 Vdc when 100% charged.

As nice as a Camaro is, it is not a corvette. It's a 12.85 lol

 

Your tire pressure is too high, GM recommends 30 psi 😬

 

GM like all modern cars, charging the battery is controlled with a microprocessor- no more simple voltage regulator! . They ONLY charge to 80% to save energy. It's good enough. In my case if I have not driven for say 4 or 5 days on the way to town (30 miles rural roads no stops) the dash voltage (actually reading the alternator output) is ~14 to 14.5 volts. It is more than enough to meet sound system etc needs and will charge the battery to 80%. Usually on my way home it will make a step change to ~13 volts. That is only enough to supply sound system etc BUT not enough to charge more than 80%.

Had this info in my file:

Fuel Economy Mode
The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amperes and greater than −8 amperes, and 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 and 13.1 V.

The BCM will exit this mode and enter Charge Mode when any of the conditions described are present.

Charge Mode
The BCM will enter Charge Mode when ever one of the following conditions are met.
• The wipers are ON for more than 3 seconds.
• GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
• The estimated battery temperature is less than 0° C (32°F).
• Battery State of Charge is less than 80 percent.
• Vehicle speed is greater than 145 km/h (90 mph)
• Current sensor fault exists.
• System voltage was determined to be below 12.56 V
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9 and 15.5 V, depending on the battery state of charge and estimated battery temperature.


Bottom Line:
Looks like 14.9 is within the 13.9 to 15.5 volts when charging. Frankly with a 2020 C8 I'd be looking to get a new battery. Just told the gal who lives in the complex where I do that bought my 2020 C8 to do just that. Even though we don't get that cold (will be 19 Wednesday morning) did not want her to be stuck. She can afford a new battery and took my advice!

 

In case you didn't learn or remember from HS physics and chemistry class. PV = nRT. Putting it simply, given V and nR remain constant for this purpose, when T goes up P will also.

Just so happened that I set my tires to exactly 30psi this morning and drove for 30 minutes before that picture was taken. Even in cooler Temps, the C8 tires will increase 2 to 4 psi as they warm up due to road friction as one drives. That is why you take and ajust tire pressure in the morning before you drive. Not during or after.

Btw, if you read the manual, if you plan on sustained speeds of 155 mph or greater, then it is 38 PSI (cold).

After my Game Changer sits over night, it'll be back to 30psi again. I'll retake the picture if it'll let you sleep easier. Just kidding. Thanks for your concern.

 

Jerry, proper charging is battery driven, not any program or "regulator" driven. Similar to eating. It's your stomach/brain relationship vs how fast or slow you move your hands or mouth.

Batteries are a chemical vs physical reaction. It is never linear. I've seen a full charge vary from 6 to 48 hours on batteries. The proper charge is 1 volt above battery current condition until 100 "saturation" is achieved.

the biggest item missing in all of these discussions is the amperage. Voltage is only part of the equation. The graph in my original post shows it. All of this is beyond my intended purpose. I was just curious about the 14.9. My C8 has never done that before. I think my battery is probably getting close to the end, but even my C8 "A" tech doesn't know. I could do a load test, but ..... no big deal unless I decide to take it for an outing, then I'd replace it before I left. Regardless, I'll be changing it this summer, unless it decides sooner.

Coincidentally, my son just had his 2.5 year old battery (Toyota OEM) replaced under warranty this afternoon. Slow to start.

 

@JerryU 's explanation in post 11 is the correct explanation for the charging algorithm, as explained in the Service Manual. The car has a battery monitor that assesses the state of charge of the battery when the car is off after it has sat for at least 4 hours, undisturbed. When the car is running, that same battery monitor measures the current in and out of the battery and estimates the state of charge of the battery. From that information, and other car conditions, it selects a charging mode, and then determines the target generator voltage. That voltage can vary quite a bit.

As Jerry noted, the target state of charge of the battery under normal conditions is 80% not 100%.

Using the information in the Service Manual, I made a graphical depiction of the minimum and maximum charging voltage for each charging mode, annotated with the conditions that cause selection of that charging mode. The voltage gauge on the DIC is labeled battery voltage - and it is the voltage measured at the battery. But when the car is running, the voltage at the battery is going to be the generator charging voltage as well - that is still the voltage measured at the battery.

 

Yep, I recall C8J has strong views on keeping a battery charged! BUT not what modern cars are doing! To save energy they are all using their computers to charge batteries under most driving conditions to only 80%. That does waste less energy.

Funny we're having a similar issue with the Li-Ion charger in E-Rays! GM recommends and sells the same Vette Logo charger for 12 volt Li-Ion battery as Vette lead acid batteries. I bought one (because I'm using my 10 year CTEK equivalent to GM charger I bought for my 2014 C7 on my street rod!) I seldom used the charger. Even when I was on vacation for 3 weeks with my two C7s and my 2020 C8 did not use a charger. The GM 2014, four volume service manual showed the car can sit ~4 weeks and starting with an 80% charge and start the car. Some parked at airports even longer. @Andybump measured the parasitic current draw in his C8 and got ~10 milliamps after the cars power saving circuits cut most power (20 to 30 minutes.) Using the 2014 Service Manual data the C8 starting at 80% charge should start the car after sitting for ~5+ weeks.

SIDEBAR
Pics is some info from tests I made after using the GM 2025 CTEK built Vette charger. When driving sufficient time to have the Li-Ion battery fully charged by the alternator and their charging algorithm it measures from 13.25 to 13.30 volts on my quality high impedance FLUKE meter. From Table below that is ~85%. The charge instructions say the last light (that took 4 hours to reach) is 100%. But it looks to be about 95%. However, I checked 24 hours later, which some Internet info said is the correct way, and it was 13.32, again about 90%. Some dedicated Li-Ion chargers can reach 14.4 volts. For some applications such as RV batteries when parked, that might be best.

There are battery "expert" opinions on the net. Most say the following:
Charging a Li Ion car battery to 80 to 85% versus 100%

• Charging a lithium-ion (Li-ion) car battery to 80–85% instead of 100% can help improve the battery's long-term health and efficiency:
• Battery degradation: Charging a Li-ion battery to 100% regularly can cause it to degrade faster. This is because the high voltage needed to maintain a full charge can stress the battery's chemistry.
• Charging rates: Charging rates slow down significantly after 80%.
• Battery efficiency: Li-ion batteries are most efficient when operating between 20–80%.
• While it's safe to charge to 100% when needed, like for a long journey, it's best to avoid doing so regularly. (MY Note: have friends with RV’s who have multiple Li-Ion batteries and when parked want the longest use possible. Not the case with the E-Ray. Also the "long trip" statement does not fit the E-Ray as when the engine is operating the 12-volt Li-Ion battery is charged by the LT2's alternator.)

BUT like most internet Info a few "experts" say the opposite! GM's reason for whoever supplies the 12 Volt Li-Ion battery may be for energy sayings. But their charging algorithm when driving only charges to 13.3 volts ~90%. With their recommended and sold Li-Ion/Lead Acid charger after a day is about the same charge percentage as the alternator and its controls allow.

Folks can decide what is best for them, even a standard lead acid charger, as many Li-Ion battery suppliers who are not pushing their own charger state "can be used but will only charge to 60 to 80%." No problem for a Li-Ion battery. To Each Their Own but until GM provides more info I would stick with their Recommended and Sold Li-Ion/Lead Acid charger. It's less expensive and discounts available thru many Internet GM parts sellers.
This is a PDF Doc with much more info and Pics:
http://netwelding.com/E-Ray_12_Volt_Battery.pdf
Includes GM part number for MY 2025 charger and where I bought for 27% discount.

I installed the MY2025 Li-Ion/Lead Acid charger after my E-Ray sat for a week.
It reached what the instructions state is 80% within seconds. When I had installed my 10 year Old CTEK charger it showed fully charged in seconds as the car alternator charges to ~13.3 volts.







The Li-Ion voltage/capacity curve is very flat so can not provide exact values. As noted it varies significancy at the extremes. But the above table provides a good indicator.

 

If it makes anyone feel better, the same discussion is taking place over on the F150 board. Not funny, but interesting.

 

This discussion is calmer than it has been in the past and is why I didn't look to reignite it again.

I only even brought it up because as a data guy, it was significant to me in that since I am an original owner with one of the oldest C8s out there, I have observed some things others may not have. I have NEVER seen any voltage above 14.2 or 14.3 on MY C* ever. This is not the first time it has been started with an OAT of 45F, but it is the first time I noticed 14.9 on the battery voltage and for more than 30-60 seconds.

The C8 techs I talked to had no positive reason for the 14.9, but my hunch is that my battery is in a normal life cycle and probably on its way out. All the discussions on charging algorithms is moot for this thread. I was just trying to figure out the sudden unexpected gauge rise. Something I was trained (gauge scan) to notice starting 50 years ago. "There are no points for second place."

As far as I am concerned, this

 

 

Yes, it could be an a "warning to replace [the battery] soon" or it could indicate a malfunction in the charging system. To make a short story long:

Given the title of the thread, Charging Algorithm, and the subsequent statement that GM is holding the charging algorithm secret, I thought the question was what is the charging algorithm. Hence the response(s) regarding the description of the battery monitor process, the charging modes, the conditions leading to the mode selected, and the generator output voltage (which will be the voltage seen on the DIC) range. There is considerably more detail in the Service Manual than presented in the posts above. Granted, there is lot unexplained. The exact algorithm by which the battery state of charge is not explained in detail - it just says calibrates itself by measuring voltage when the car is off, then measures current flow into and out of the battery to keep a running estimate of the battery state of charge, then uses that as one factor in selection of the charging mode. How its estimated is not explained. And there are other conditions besides state of charge that are factored into the charging mode selection.

But apparently that was not the question. Rather it was, why, after all this time, I am seeing 14.9 volts when I never saw that before ("My battery is still the OEM from July 2020 delivery. Any chance it's giving me a warning to replace soon?). So, the question, in bold, is inviting speculation about what is going on with the battery, rather then whats going on with the charging system. So, here's a little speculation. And, its based on the assumption that the description of the charging modes in the manual is accurate -

What's going on with the battery that causes the generator output voltage to be 14.9 volts? My approach is to look at the charging system to determine what battery condition might cause it to produce the observed 14.9 volts.

There are only two charging modes that will result in a generator output voltage of 14.9 volts. One is the Battery Sulfation Mode. The Body Control Module (BCM) will enter this mode when the interpreted Generator output voltage is less than 13.2 V for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2-3 minutes. The Charge Mode voltage can range from 13.9 to 15.5. Considering that most of the time in steady state, the BCM will select the Economy Mode which has a voltage range from 12.5 to 13.1, I would expect the Charge Mode to be entered for 2-3 minutes out of every 45 minutes of running. It does not mean that one would see 14.9 volts, but it does mean that one will see a voltage between 13.9 and 15.5 volts, every so often.

The other charging mode with that voltage range is the Charge Mode. The BCM will enter Charge Mode when ever one of the following conditions are met:
1) Windshield wipers are ON for more than 3s.
2) Climate Control Voltage Boost Mode Request is true, as sensed by the HVAC control module via serial data. High speed cooling fan, rear
defogger, and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
3)The estimated battery temperature is less than 0°C (32°F).
4) Battery State of Charge is less than 80%.
5) Vehicle speed is greater than 145km/h (90mph)
6) A current sensor malfunction exists.
7) System voltage is determined to be below 12.56V
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9-15.5 V,
depending on the battery state of charge and estimated battery temperature.

So, if the voltage on the DIC is now reading 14.9 or higher consistently, it would appear that Charge Mode is being selected consistently, rather then the Economy Mode which maintains the battery at 80% charge, and shows voltages between 12.5 and 13.1. What would cause that? Ruling out conditions 1,2,3, 5, because they are not issues with the battery, leaves condition 4 (state of charge less than 80%), or 6) current sensor malfunction, or 7) system voltage less than 12.56v. Note that in the Economy Mode, the indicated voltage is between 12.5 and 13.1 - so if it drops to 12.5 in Economy Mode that would trigger the Charge Mode. Its not clear to me if that (dropping to 12.5 volts in Economy Mode) would indicate a battery issue, but it could, I suppose.

Not profound, nor do I claim it to be so, its a possible malfunction in the current sensor, or for whatever reason, the car is consistently estimating the battery state of charge to be less than 80%. That could indeed indicate that there is an issue with the battery that is preventing it from charging to 80%. This is where more detail on the algorithm that estimates the state of charge would be useful, but we don.t have it. So, all we know is that either the battery actually is not charging to 80%, or the the car incorrectly thinks the battery is not charging to 80%.

So, yeah, it could be a warning that the battery is aging, or it could be a warning that there is an issue with the current sensor or the process used to estimate the state of charge of the battery.

 

Today the systems are more complicated and have much more functionality since they are digitally controlled. PWM controlled alternators have been in use since the early 2000's. The voltage is also digitally controlled to improve the efficiency of the system. The voltage ceiling is set higher so the alternator can be throttled, and the devices can still draw the same number of watts. The alternators' primary function is to supply the devices with power and the battery is just one of the devices.