Below is a typical lead acid battery voltage vs state of charge chart. Any time the open-circuit volt is at approximately 12.5V it is 100% charged. What I would like to know is why did Chevy put a flooded battery in instead of an AGM battery.

 

Sorry. 12.6V I am a crappy on a keyboard

 

Thats right. A recently charged battery, right after charging, will read a higher voltage. The OC voltage in those charts must be measured after the battery has set without a draw for 4 hours, in order to assess the state of charge. The car actually does that, by the way. After it has been off for several hours is will calibrate the Battery Monitor Module, then when the engine runs it measures current into and out of the battery to keep a running estimate of the state of charge, which it uses as on of the factors in selection of the charging mode. The voltage range for the Economy Mode is 12.5 to 13.1.

 

Cost! Your job to add as a replacement.
What I used as a replacement for the OEM in my 2008 C6. Since the car was yellow used an Optima Yellow Top!
Used a Diehard AMG as a replacement in my 2014 C7

Installed an Optima AMG in my street Rod with it's 8.2 Liter BB built in 2000.

 

That's interesting. Based on what Andybump says about the battery monitoring system, it doesn't seem to monitor battery "life" per se, just state of charge. I am used to having to the tell the system (BMW or Porsche) when I change the battery, what it is (Flooded, AGM, Li Ion) Ah rating and CCA. The 2021 service just replaces the battery. Normally the charging profile for an AGM battery is slightly different than flooded. It normally uses a slightly lower voltage in almost all cases.

 

I have read the same thing and its a valid concern. I was not dismissing it. But it remains the case that the normal charge is going to be 80 percent. The chart shows the conditions listed for each state, and "less than 100% charge" is not one of the conditions. I include state of charge as a condition where it is mentioned as a condition - if its not listed - then state of charge was not a condition for selecting that mode. Thats the point. The car will enter the "charge mode" if the speed greater than 90 mph (thats not typically happening), or if cooling fans are on (thats not all the time), or a current sensor malfunction (thats rare), or the wipers are on (thats almost never for Corvette drivers), or if the state of charge is below 80%. Below 80% charge is the primary condition. The start mode only last for 30 seconds after start, regardless of state of charge. So generally, under steady state conditions, its going to be in the economy mode, which attempts to maintain the battery voltage, neither charging or discharging it - which I interpret to mean it maintains it at 80%, because greater than or equal to 80% was the entry criterion. If it enters at 80% its going to maintain it there - as I read it. It has a current sensor that measures current in and out of the battery so it can adjust voltage as needed to accomplish that.

If the vehicle has entered the sulfation mode, even for the three minutes, or if there has been a request from the HVAC for the boost - its true that the battery might charge beyond 80% but that not going to be generally true. You can let the car sit off for 4 hours, and then check the voltage at the battery without triggering the car systems to see. I measured the parasitic current here

https://www.corvetteforum.com/forums...e-battery.html

Its only 10 ma after the systems fully shut down - which takes 10-15 minutes. But, if you unlock the car, or open a door it will trigger the systems to come back on, and that draw is on the order of 10 amps even with external lights off. I should have measured the voltage but I did not. My bet is if you leave the car off a charger, just drive it, then shut it off, and measure the voltage after the car has been off for 4 hours, and you dont trigger the systems, you will get a voltage consistent with 80%. Of course, if you trigger the system, you will measure even less.

 

Hmm, the Optima AGM's have a slightly higher voltage.
The Optima worked fine in my 2008 C6 and the Diehard AMG worked fine in my 2014 C7.

 

Yes - apparently it does not require any change to the charging system - even though the voltage vs state of charge is slightly different. I found no indication in manual that its necessary to tell the system about a new battery or different battery type. There is a scan tool parameter in there for battery type, but the expected value for that parameter is "default" even though there are other choices. Its not, according to the manual, set to FLA. I think, and this is speculation, that the when the car calibrates the Battery Monitor Module after a battery replacement (or any time) after it sits for a few hours, it will probably make a slight error in assessing the state of charge of the AGM - and when charging it wont achieve quite the same state of charge as intended for the FLA. But the difference is negligible. It does have access to both voltage and the resulting battery response (current) so it might adapt that way, but there is no stated evidence for that. Folks have reported using AGMs and also AntiGravity LI batteries without issue.

 

Right. Meaning at 80% the Optima voltage is bit higher than an FLA at 80%. Which means, if it does not adapt, it will overestimate the state of charge of the AGM, and thus undercharge it with respect to its target state of charge, be it 80% or 100%. For example, in the attached charts the FLA OC voltage after sitting a while is 12.41 at 80% charge. But the AGM will produce 12.41 volts at 60% state or charge.

 

@rxscram , after reading everything you wrote, and everything I wrote, and the description of the Fuel Economy Mode, I agree that there is nothing in that description that says it will not charge beyond 80 percent. I continue to believe that the for the majority of the running, the selected charging mode is the Fuel Economy Mode. It will enter that mode if the state of charge is above 80%, and in that mode the voltage range is 12.5 to 13.1 volts. There's no further indication of how the voltage within that range is selected. 12.5 is less than 100%, if it tapers to that voltage, and is then shut off, thats already less than 100% per the charts posted in this thread - and after 4 hours shut off, it will drop below 12.5 so I think that could result in a measurement of 12.41 after 4 hours. But since it can go as high as 13.1, its possible that it can charge beyond the 80%. Its just not clear from that description. There are many others on the forum that claim it does target 80% - I don't know if that is based on the charging system description or other sources.

Having said that, the discussion started (as a diversion from the original OP topic) because a discussion about run down time - and I suggested that one should not assume that the battery has been charged to 100%, and should not assume that the usable run down time can be all the way to 0%, but rather should base it on assuming an 80 % state of charge, and should not allow the battery to discharge below 50 percent. I still think thats a good idea - and for whatever reason its also exactly the example that the Service Manual uses, showing discharge time vs current going from 80% to 50%. That example tended to further my belief (right or wrong) that the target state of charge is 80%.

 

^^^^
Yep, modern cars only charge the lead acid batteries to 80%.

These are the Google AI answers to these questions:

• Results fordoes charging a lead acid battery to only 80% save energy
• Results forwhy do modern cars only charge battery to about 80%

Google AI AI answers:
Yes, charging a lead-acid battery to only 80% can generally save energy compared to charging it to 100% because the most significant energy loss occurs during the final stages of charging when the battery is nearing full capacity; by stopping at 80%, you avoid this inefficient phase and can extend the battery's lifespan as well.

Modern cars, particularly electric vehicles, often only charge their batteries to around 80% because charging to 100% can significantly shorten the battery's lifespan by putting excessive stress on the battery cells during the charging process; this practice is known as the "80% rule" and helps maximize the battery's longevity over time.

I also asked if my 10 year old CTEK Model 3300 can charge an AGM battery

Google AI answer:
Yes, a CTEK Model 3300 battery charger can charge an AGM battery; CTEK chargers are designed to work with various battery types, including AGM batteries, and are considered suitable for charging and maintaining them properly.

Key points to remember:

• AGM compatibility:
  Most modern CTEK chargers, including the Model 3300, are designed to be compatible with AGM batteries.

This is the AI answer to another question I asked about the 80% charging Rule for Lead acid batteries:
AI Overview:

The "80% battery rule" for lead acid battery charging means that it is generally best practice to only charge a lead acid battery up to around 80% of its full capacity, as charging beyond this point can significantly shorten the battery's lifespan due to increased stress on the battery plates and excessive gassing; the last 20% of the charge should be done at a lower current to avoid damage.


MY GUESS:
It's possible the C8 (and probably C7 80% charge algorithm) does charge the battery to 100% for a short time. What I found the capability of charging to 15.5 volts, more than enough voltage) for a short time to avoid the only issue I have read of constant and only 80% charging: sulfation. But it appears that periodically charging even for a short time to 100% may be sufficient to do that.

i am No battery expert but like all of us, with EV and Hybrids becoming more prevenient we'll have to be versed on the issues!

SIDEBAR
They are currently building a 3.2 billion EV/Hybrid manufacturing plant ~10 miles from my home in Florence SC. It is unbelievable how fast this huge facility and employee training center is being constructed. We're in NE SC and the plant will supply the 11,000 BMW employees in the 8 million square foot facilities on 1150 acers in Western SC. They make all the SUVs for the world in the facility. They ship to 120 countries some ~250,000 each year at a ~10 billion dollar value. (For 2023, BMWtotal sales from SC were 362,244 vehicles for total revenue of ~$27 billion.)

They are "pushing" PHEVs. Wife is on her 3ed BMW X6 SUV. The 2025 she received October 5 (~$4000 Option) has only had the gas tank filled once. And that because we had to make two 250 mile round trips to Charleston to visit a friend. Most drives are >45 miles round trips to town. All done on battery power. It has the same 335 hp twin turbo I6 ICE with 190 hp electric motor in the transmission. Same mechanical AWD as her prior 3. With the combined power C&D test 0 to 60 test was 3.9 seconds. Great for a heavy SUV.

And no knew electric power capacity, power lines needed by Duke Power! We charge at the Off-Peak electric rates when they have plenty of excess power capacity. Those electric rates are half the On-Peak rate. And to my surprise where that used to be from 9PM to 6AM with the advent of solar power in NE SC plants, homes the On-Peak high rate is only 6AM to 9AM. There is a special even lower "discount rate" of $0.05/KWh from 12 noon to 6PM! That is ~1/3 the on peak high power rate.

Can understand the concern of having only an EV BUT no such issue with a Hybrid. I had a 240 volt plug in the garage for a welder and with max 20 amps (I actual set the car charge rate for 16 amp max rate and the 27 kWh battery charges from zero in ~6 hours. Can charge in <3 hours if you install a 240 volt 32 amp power line - similar to an electric stove- the charger that comes with the car is capable of handling.)

Yep they way I use my Vette, local driving, can't wait to order what I expect to be available well before 2030 an EV Vette with 0 to 60 in 1.9 seconds!

 

Please, folks, let's stop relying on AI answers... they're often wrong, particularly as the questions becomes more technical.

As rxscram mentioned earlier, you generally want to top off LA batteries to prevent sulfation over the long term (which is what slowly kills your long-term capacity, and why LA batteries need to be stored fully charged, ideally with a tender for more than a few months of non-use). There are a couple of values listed that I believe are getting confused/swapped (no to mention Li-ion technologies appear to be getting mixed into the results)... LA batteries below 80% capacity are considered approaching EOL. During charging, your charge rate is typically 0.7-1.5C for the first 70-80% of charge... after that, things need to drop down to ~0.3C to avoid O2 generation until you're nearing 100%, and then it drops down to a trickle charge to deal with internal resistance losses and self-discharge rate. But you still want to charge to 100%, not stop at 80%...

 

^^^^
Yep have said the same re AI! Have to be careful.

But I have been involved the power industry from when I was in college. When I graduated started in R&D in an unrelated industry (frankly saw too much waste and featherbedding in my two college power company summer jobs. That has changed today.) Invented a 3000 amp Submerged Arc Welding system used by steel companies to fabricate much of the high pressure natural gas and oil pipe 16 inch diameter and larger that is in the ground in US and Canada today!

A few years ago visited with my local ASME Section (which I Chair) the local Duke Power generating complex where there in a nuclear power plant, an older coal fired power plant they were taking out of commission and where they had 6 (no doubt more now) Natural Gas Turbine generates the largest size shown below. They can be put on line in a very short time and can be installed about anywhere. No need to transmit power foolishly from 15 miles off shore in 500 foot high wind turbines to Kansas with the inherent I2R losses! Nope now that we have a smart energy policy the 16% coal now being used to generate electric power in the US will all switch to Natural Gas IMO (~1/2 the CO2/BTU of coal.). We can supply that gas to Europe, India, China etc as is being done to some degree now. But between the US and Canada we have 100+ years supply of Natural Gas.

RE batteries suggest watching the Jason Fenske Video in my post #40, to see what Tesla's guru on battery power shows why 50% charging is logical. Granted that is for LiFePO4 batteries which will soon replace lead acid one way or another anyway. BUT most car companies are charging lead acid batteries to 80% for energy saving reasons. My Guess is they manage any sulfating issues by periodically charging to 100% but on average 80%. It's all computer driven, easy to do. And as I showed in an early post the C8 has the capability of charging to 15.5 volts when desired. But admit I'm a mechanical gear head and just studying to better understand batteries. Jason Fenske has a number of video's on the subject I have watched. Easier and more fun watching then plowing thru tech papers!


Yep future IMO of power generation. In addition to solar and some wind power where logical (not 15 miles off all US Shores) Natural gas turbines can be quickly placed wherever needed to feed existing power grid. Charging cars can mostly be done where there is excess capacity. We can ship liquid natural gas anywhere as we are to some degree now. Can replace the coal we're currently shipping my rail from the East Coast to West Coast ports to send to China! Will cut their CO2 emissions in half!

 

Jerry,
Thanks for that! I rarely if ever quote the AI answer, but the answers usually have footnotes that lead to the actual sources. And some care is needed to insure that the material is discussing a lead acid automotive battery. I found some supporting documentation that is not AI generated (no pun here). And the supporting documentation does support what it says - about 80% charging being efficient, prolonging the life, but needing to occasionally charge higher to deal with sulfation.

The Sulfation Mode, described in the Service Manual, appears to provide that occasional higher charging rate - and it name offers a clue as to its intent. Note that the voltage range for the Fuel Economy Mode is 12.5 to 13.1. The Sulfation Mode (which invokes the Charge Mode) will be invoked if the voltage is less than 13.2 volts for 45 minutes. So, in the Fuel Economy Mode, the Sulfation Mode is guaranteed to kick in for 3 minutes out of every 45 minutes - and then the voltage range is 13.9-15.5.

This non-AI source https://www.victronenergy.com/live/drafts:battery_life says
"It is safe to cycle a battery between 50% SOC and 80% SOC – it is quite efficient to do so, too. But this kind of cycling cannot be continued for extended periods. Recharging a drained battery to about 80% state of charge can be achieved quickly – but returning a battery to 100% SOC takes much longer because the rate at which it can accept charge is very much reduced as it approaches full-charge. It is important to allow the necessary charge time to return a battery to 100% SOC at least once every 30 cycles – that’s monthly for a battery which is in use every day. There are several reasons for this which we will cover a bit later."

This source https://poweringautos.com/how-does-l...fect-charging/ , specifically about lead acid automotive batteries says
"Lead acid battery ageing reduces capacity and increases internal resistance. This affects charging efficiency and may lead to sulfation. To extend shelf life, keep the charge between 60-80%. Regular topping charges help maintain voltage."

None of this "proves" that the target state of charge for the Fuel Economy Charge Mode in the C8 is limited to 80%, but a charging system that maintained an SOC of at least 80%, with occasional charging to a a higher level via the Sulfation/Charge Modes would be consistent. It pretty telling that the name of the charge mode is "Fuel Economy Mode". It might charge beyond 80% - it never says its limited to that - but if it does go beyond 80%, it is at a limited slow rate, based on the voltage range and the description. That is, once the battery reaches an 80% SOC, the C8 charging system switches (most of the time) to the Fuel Economy Mode with a much lower voltage range and is described as not charging but only maintaining the battery open circuit voltage (their words not mine).

My original point was simply that one can't assume that when the car is shut off, that it has charged the battery to 100% state of charge, for the purpose of calculating the useful rundown time, if stored without a battery maintainer for any length of time. Better to calculate it based on the run down time from 80% to 50% as offered by the example in the Service Manual. If I get energetic enough, I will measure the voltages to see whats going on.

 

^^^
Andy I recall this was a forum issue in 2014 when folks realized the battery was being charged only to 80%. But it was known many car companies were doing that for energy efficiently. That was before AI! I recall discussing the subject with the EEE (that's an EE with a Master's ) from our R&D Lab who comes to our Tuesday retiree luncheons. He validated the energy savings and was skeptical of claims that it extended battery life.

Frankly energy savings are very important to car companies, each ~0.1 mpg helps their EPA mpg numbers. Battery life once past the warranty not their concern!

Heck a Lead Acid battery is cheap enough and is going to fail! A year or so earlier is not a big deal!

I had replaced my 1st Vette, a1988 battery within a year since the car had no low parasitic current draw circuits. Twice I tuned on the interior lights to get something in the car when I pulled into the garage at night. Since they had a 30 second time delay after the door was open on the high wattage interior lights, thought nothing of them being on when I closed the door from the garage to the house. Both times dead battery in the morning!

My 2008 C6 battery failed within a year. GM was smart enough to include a plastic open duct in the engine compartment battery holder as their were some power electronics right below and if the case failed (mine did with a crack on the bottom) the acid could eat the electronics! My C6 was yellow so bought an Optima Yellow Top to match! My S-10 truck battery case also failed. That OEM battery had front posts and if the screw was tightened too much it cracked the case!



I was one of the 1st on the Forum to replace the battery in my 2014 C7. Had ordered right after the launch at the Detroit Auto Show in Jan/Feb 2013. Was one of the 1st delivered to Hendrick in Cary NC. Only dealer at the time who would take a deposit not knowing the MSRP with an email saying that would be the price! GM didn't release the price until ~May. Mine arrived late August 2013. It had a low voltage from day one but local dealer just said it's fine. By year two voltage had dropped and before year 3 winter I installed a Diehard AMG. Recall despite having the Four Volume Service Manual it just said remove cover over left side of battery but no clue as how! Turned out needed to push a screwdriver into recesses to release the plastic clips!


The real trick, in addition to getting the battery out of it's hole was accessing without ripping the untrimmed carpet under the plastic wheel well cover. Some posted dealer tech ripped their carpet. Wasn't hard. In my How To Doc PDF I showed how to remove the front of the plastic inside wheel cover so that the carpet could be slipped out without tearing!

Yep if you plan to keep the C8 plan on learning how to access and replace the battery. Those with AAA who think I'll just call them when the battery dies in the winter might find with a C8 the tech will break the two side plastic covers in the Frunk that need to be removed. At least learn to do that yourself before they come! Need to pull to center of car NOT UP or you'll break the clips!

 

As we have digressed from my original meaning / question.

The 80% "rule" is actually 85% in reality regarding charging lead acid batteries - AGM or Older Wet cell. The reason is that to run an engine / generator / alternator to achieve the last 15% top off charge (as I mentioned earlier) takes from 6 to 48 hours because it is a chemical vs direct physical event. This is normally applied to situations that are not being done when connected to a shore based power grid like when traveling on a marine vessel. Power cords are not long enough - pun intended.

So one can do the bulk and acceptance phases relatively quickly - typically 30 - 60 minutes, but the 3rd phase float takes the 6-24 hours to get from 85% to 100% charged and it is not practical or efficient to keep an engine running when not being used concurrently for propulsion to just charge a battery(s). So when not moving in a boat (power or sail), full charging is typically stopped after reaching the 85% charged level. This is also why it is recommended to go to a dock and connect to shore power (at least weekly) to allow for enough time to completely reach 100% to prevent sulfidation on the battery(s).

In the case of automobiles, there is no reason for this philosophy or procedure to be employed as the engine is already running for propulsion and not just battery charging so there is no wasted energy or fuel to just keep an engine running. You do not run a boat engine to charge batteries while anchored - not moving. one would use a dedicated generator for efficiency - and a DC generator vs AC generator at that - another story not for here.

The supposed overall 0.1 mpg increase in the C8 mpg rating for the EPA rules makes no sense either because the C8 is not manufactured in enough numbers to make a dent in that for Chevy or GM. BTW, my 2022 GM Acadia still does the "old" correct charging profile - 14.2 Vdc until charged then reduces to 13.2 when complete.

So the reasoning still is unknown to all of us as to why they are doing this. It truly makes no sense (affect) other than to reduce battery life.

As long as some still want to post erroneous data, AGM and GEL have completely different charge parameters. AGM and Lead Acid are nearly identical (within 0.1Vdc) on their charging parameters. AGM and standard wet cell batteries are 100% charged at 13.2 Vdc for professional manufacturers, 12.85 for budget manufacturers and 12.6 for substandard manufacturers of Lead Acid batteries. This is why you any see these different % charge tables. The C8 and every other vehicle is worthy of a credibly manufactured battery.

Lifeline uses 2.2 Vdc per cell (13.2 - 12vdc battery) in their batteries, but is showing a range to cover many manufacturers. They mention 2.17 at the bottom for their batteries after aging (typically after 24 months). i can verify from actual use and installing verification in thousands of locations.




The above Lifeline (Best AGM batteries manufactured) document may be found here.
https://lifelinebatteries.com/wp-con...al-5-06-19.pdf

 

100% agree and posted as I was doing my reply.

I just don't think the 0.1mpg is significant due to the low apx 30K /year of this vehicle. They certainly do not worry about battery life once past the warranty - not their concern.

 

Yep, don't know if it's 0.1 or 0.01 but do know the auto manufacturers kill for any power savings to get a higher EPA mpg! (Skip Shift on my C6 and two C7 standard shift Vettes were a good example. Really only an issue in the EPA mpg drive cycles. Not an issue for most all normal driving.) If it's only affecting battery life after warranty no GM concern!

 

No disagreement with what you said. But regardless of whether it makes sense or not, the name of the charge mode, Fuel Economy Mode, suggest that GMs reason for that charge mode, whatever it does, is fuel economy. Its entered when the state of charge is at or above 80%, and it either maintains that state of charge around 80%, or slowly charges beyond that. Because it stated that it neither charges nor discharges the battery in that mode, I originally assumed that meant it maintains it at 80%, but reading other interpretation of it, I now agree that it never says its limited to 80%.

I suppose they could have named it the Battery Life Reduction Mode.

 

Still doesn't make sense with the low volume (compared to the entire fleet of all makes and models in GM), they could get more of an EPA mpg by reducing tire footprint by 0.1"

Simplified, because most ICE technologies (ICE, streamlining, ...) across all manufacturers, are close enough for MPG results, that the biggest factor is directly proportional to weight alone. My GMC Sierra was twice the weight of my son's Honda and it got 1/2 the mpg at similar speeds. My 2016 Malibu had the same weight as the C8 but it got apx 33% better mpg due to the difference in the C8 tire size and its rolling resistance affects on mpg. There are many variables engineers can investigate when designing, but battery charging is such a minor issue vs its detrimental affects is not seeing the trees in the forest.

Defense (or prosecution) rests.