This is a topic I have followed closely after reading the 2012 Government Plan to cut CO2 emissions in ~half by ~doubling the mpg by 2025. That was to be done with agreement by most auto manufacturers stating an aggressive redaction in mpg BY CAR FAMILY. It was a very well written report that define BY CAR FAMILY what each would be required to achieve. At the time Toyota was pushing Hybrids as a method all could use. Some said they would use EV's to reach the goal, one was Porsche. The goal for the Corvette Family was ~39 mpg. (It would be similar for most high powered 2 seat sports cars. It was a complex formula-but logical.) A high powered car that could carry 4 folks could have a lower mpg goal. A "Grocer Getter" with lighter weight and low hp engine could do much better so the goal was higher. NOTE it was not by Manufacturer so Ferrari could not buy Tesla to lower their average mpg. It was strictly by "Well Defined Car Family." Also it was not driven by a "Gas Guzzle Tax. They were NOT going to let rich Corvette (Ferrari, Porsche) Owner's destroy the World while others sacrificed! It was a prohibitive Tax of the Manufacturer And not just the name Porsche Sports cars were in a different defined family than a Porsche labeled SUV.

I read the report. it was well done and pretty fair.

These were some press releases in 2021, the 2022 when a new pen signed new goals:

WASHINGTON December 2021– In a major step to fight climate change, the administration is raising vehicle mileage standards to significantly reduce emissions of planet-warming greenhouse gases, reversing a Trump-era rollback that loosened fuel efficiency standards. A final rule issued Dec. 20 would raise mileage standards starting in the 2023 model year, reaching a projected industry wide target of 40 miles per gallon by 2026. The new standard is 25% higher than a rule finalized by the Trump administration last year and 5% higher than a proposal by the Environmental Protection Agency in August. “We are setting robust and rigorous standards that will aggressively reduce the pollution that is harming people and our planet – and save families money at the same time,” EPA Administrator Michael Regan said. Details to come. (MY NOTE: little doubt those details were going to be announced after this past election! We'll see just what happens I expect in January. BTW in 2017 when the plan was canceled with a Pen, California supported by 5+ other states sued the government and it was died up in court. Expect as then it will NOT BE, drop all mpg goals. The EPA shows car companies have made little progress and must do better. We'll see just what happens.

Washington, April 1st, 2022 49 MPG Fuel-Economy Standard Ordered for Cars by 2026 The Biden administration ordered carmakers to increase their average fuel economy to about 49 mpg by 2026, in an ambitious effort to make up for progress stalled when President Donald Trump rolled back the efficiency program. The new fuel economy rules, issued April 1 by the National Highway Traffic Safety Administration, require carmakers to heighten the fuel efficiency of their fleets by 8% annually for the 2024 and 2025 model years, and 10% for 2026, according to a senior administration official. The agency was facing a March 31 deadline to finalize new rules for the 2024 model. Putting the new numbers in perspective: The EPA reported in November 2021 that carmakers achieved an average of 25.4 mpg for vehicles made in 2020. That was 0.5 mpg higher than the 2019 model year and a record high, but a far cry from the 49 mpg by 2026 that President Joe Biden’s is now proposing. In real world mpg terms, 39 mpg is what is estimated 49 mpg EPA values will achieve.

This is a summary of the 2012 government plan showing we have affected the Corvette. A hybrid Vette could have met the goal in EPA tests. (if you want to know how this is my DOC, defining as a PDF: C8_FWD_Hybrid.pdf ) Ferrari in 2013 started to make hybrids. Like GM the 1st, Performance only Hybrids until a government US/Europe required higher mpg. That required forced Stop/Start and not turning on the ICE until in EPA test the electric motored accelerated the car to cruising speed (per Newton's Laws, that is where much energy is required in the EPA tests, accelerating!) Note the Mustang below the Corvette in these example numbers only required achieving 31 mpg since it could transport 4 folks. As I said most car manufacturers contributed to this report, understood the reduced CO2 emission goals.

 

There is a technical paper entitled "COST, EFFECTIVENESS, AND DEPLOYMENT OF FUEL ECONOMY TECHNOLOGIES FOR LIGHT-DUTY VEHICLES National Academies of Sciences, Engineering, and Medicine. 2015. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, DC: The National Academies Press. https://doi.org/10.17226/21744."

It dated 2015, and there might be later paper, but its in part the basis for some decisions that were made. It covers all sorts of technologies including motor oil, variable valve timeing, cylinder deactivation technology, supercharging, aerodynamic, rolling resistance (tires), on and on and on. It can read for free here:

https://nap.nationalacademies.org/read/21744/chapter/1

It does mention batteries but as far as I found its in the context of EV technology. I looked for, but could not find any discussion of charging the 12v starting battery at 80% versus 100%. It may be there, but I could not find it. So, it certainly did not make the top 10 list of fuel economy reduction techniques in that paper.

And again, regardless of the reason or the technical sense it makes, or the impact it has, GM named one of the charging modes "Fuel Economy Mode" and it appears that mode either maintains the 80% state of charge, or results in a charging rate that slow and may or may not achieve 100%. That can be checked one day by one of us. Whatever the reason, I think what we need to know, when thinking about attaching battery maintainer or doing a calculation of run down time in storage is that the car may not be charging the battery to 100%. This is all interesting to me, but from a practical point of view moot because whenever my 2021 is in the garage its on the CTEK device, which does take it up to 100% (for better or worse). I'll get motivated one day, disconnect the charger, takes some measurements, then drive the car, leave it sit for 4 hours (when the parasitic draw is only 10 ma) and check it.

On the OPs original subject, a change in the observed charging voltages on the DIC is likely an indication of a change in the battery (already said before, I know) which is likely the result of the battery aging. As noted, 14.9 volts, when not previously observed, is not necessarily an indication that the battery is being overcharged, but it might be an indication that system thinks the battery needs more charging than it previously did - like maybe its estimate of the state of charge is now generally lower than before.

 

^^^^
It doesn't appear to me connecting a charger to a Lead Acid battery that chargers to 100% should create an issue.

However for a Li-Ion (LiFePO4) battery, Tesla's Guru on Batteries report shows that is NOT A GOOD THING! If connected for a long time you are better at lower than 100%!

The GM alternator in my E-Ray charges to about 85 to 90% as does the CTEK charger GM sells for the E-Ray!

 

There was a hypothetical theory (by @RKCRLR) that if the car maintains the SOC at 80%, and the maintainer takes it to 100%, its a battery "cycle", and "cycles" is what may shorten the life.

The GM literature says use the maintainer if the car won't be driven for more than a week. Although a lot of folks have pointed out that one can go much longer without using a maintainer, I'm really starting to think the one week "rule" makes good sense. Why? Sulfaction - the topic brought up by several in this thread. Apparently, when sitting for a while in partially discharged state, sulfation build up is an issue. Its resolved by at least occasionally charging up to 100% according to several sources. The battery maintainer is one way to do that. But if the car is run at least once a week, we know that it will invoke the 'start mode" for 30 seconds, and it will invoke the Charge Mode (if the SOC has dropped below 80%), and will invoke the Sulfation Mode as well while running addressing at least partially, if not fully, the sulfation issue.

 

^^^
Hmm, had only seen that "one week" mentioned in the 2024 Owner's Manual and ONLY for the 12 volt Li-Ion battery!
First there is no Sulfation in a Li-Ion Battery! The 2025 Owner's Manual eliminated that statement. See lower Pic I made:

Second, with my E-Ray 12 Volt LiFePO4 battery tests have found the alternator only charges to ~13.3 volts which is ~90%. The GM Recommended and sold Charger is for both Li-Ion AND Lead Acid Batteries. The same one sold for all 2025 C8's. I found after 24 hours after charging (which is recommended to check battery voltage after charging, it is also ~13.3 volts. Note it was only 13.37 volts immediately after the charger showed fully charged and unplugged.

Some dedicated Li-Ion chargers can change to as high as 14.4 volts. If using in an RV and want max capacity when parked, might be useful. Jason Fenske has a number of video's on EV and other Li-Ion batteries quoted what Tesla calls their secret weapon when it comes to Li-Ion batteries, Jeff Dahn. His lab has done a lot of research for Tesla (and I'm sure others.) He's a PhD Physicist.

He discusses the dichotomy of charging to 100% versus a lower level. He shows why Ford for example would say charge to 100% about once a week. It has to do with estimating the charge percentage, important to EV user. However Ford also states if charging for a long term only charge to 50%! He quotes the Jeff Dahn report which in extensive testing even charging to the same capacity of 0 to 25% and 75 to 100% the high charge level reduces battery life. Jason goes on to explain the technical reason. He also explains why I found when installing the GM charger it went to 80% charge instantly from my 13.27 volt start BUT took 4 hours to charge to 13.37 volts. His analogy is great, the negatively charged Lithium have to find a place to "park" in a crowned lot!

PS: Jason (Engineering Explained) is a mechanical car expert. He states in the video he has been reading many electric power vehicle technical articles. He has made a number of related video's. Now with my HEV E-Ray and wife's PHEV BMW X5 SUV (where in two months have only filled the car once with gas because we made two ~225 mile trips to visit a sick friend.) The remainder of the total 1443 miles were all ~40 to 50 mile local trips/day have all been on battery, charged when plugged in at night on low cost Off-Peak power cost! Trying to lean more about the technology and better Jason reading all the tech pubs than me, and summarizing in videos!

This is one clip from The Jason Fenske video. He quotes tests made by a person Tesla quotes as their secret weapon in battery technology, Jeff Dahn. They have sponsored some of his work. He notes Ford says charge to 100% about once a week so can properly calibrate the battery capacity display (important to an EV owner.) BUT they state for long term storage only charge to 50%! Dahn's tests show that has much battery life!


GM fixed the 2024 Owner's Manual misstatement in 2025. Was not logical to have to charge a Li-Ion battery every week. It lead to speculation (including by me) that for some reason the E-Ray had a high parasitic current draw Tadge Juechter admitted that was not correct but until the 2020 Owner's Manual there was still speculation!



RKCRLR's speculation is interesting BUT IMO the GM misstatement re the Li-Ion 12 volt battery did not relate to Lead Acid Batteries. No explanation of why it was in the 2024 Owner's Manual. Putting the E-Ray 12 volt Li-Ion battery on a charger weekly is not logical. As Tadge agreed in the Jay Leno video and his statement to me in an Email, quoting: "Li batteries are actually better than lead-acid for sit-time." All reports reports say is true, with some stating it can "sit" for several months and still start the car.

 

Jerry, the RKCRLRs hypothesis and the 1 week thing both were in context of the FLA battery, or course. The literature to which I referred, where that statement appeared and still appears, is the Getting to Know Your Corvette, that I think may still come in the owners package. Attached is the statement found in the 2025 version of that. It does not, but probably should have a comment regarding its applicability to the LI starting battery in the e-ray.

The manual I have for the CTEK that came with my 2021 say its is ok for LI batteries. That was pre-eray but think it might be true for the battery in the eray - but I'm not sure its true for all LI batteries - the AnitGravity battery webiste says their battery can drop right into a car that was using an FLA with no issue and no adjustment to the charging system, but also says that for external charging, it requires a "special" charger.

This is from the Getting to Know Your 2025 Corvette






This is from the manual that came with my C8 CTEK device

 

What year is your C8 CKET charger?

 

Below is the charging profile for a CTEK MXS 5.0 which has the model number as the Corvette charger (1090), shows slightly different charge times to 80%. I suspect that the Corvette charger is a subset of this. But what is interesting is that the Corvette charger says that it is for lead acid and lithium batteries 14-160Ah on the cover.

 

Curious what year that is or about what year bought. Because for folks getting E-Rays no need to buy another charger if they have that one.

 

The Corvette charger I have came with my 2024 SR Z51. Box has GM part number 85530676 with code GR 02.215

 

@JerryU mine came with my 2021 C8. No date in the instruction manual. It says the model is Corvette(1090).

 

^^^
Thanks @Andybump So for folks getting an E-Ray who have a charger for a C8, no issue, it states for Li-Ion batteries.

The issue raised with CTEK chargers having a Desulphating Cycle is also now shown by Member @rxscram 2024 Charger Instructions to be fine as it states not only it is for combo Li-Ion/Lead Acid it shows the same Desulphating cycle as my 10 year old Model 3300 CTEK that states is for Lead Acid chargers but shows the same 1st stage Desulphating circuit. But as I found that cycle is bypassed after a CTEK resistant check shows the battery is not a high resistance sulphated battery.

What funny is the 2024 Corvette Logo CTEK made charger has the graph with the cycles as my 10 year old Model 3300 charger. BUT my 2025 GM charger I juts bought has a very few page instructions with no such charging cycle graph. It has many multiple language pages and the usual Safety and Caution pages!

So IMO all CTEK charges should work. Perhaps older ones not spec'd for Li-Ion will have a low initiating charge of ~13.0 volts BUT that is more than enough to start the E-Ray. The alternator would then charge to 13.3 volts ~85 to 90%. That is the same level as the current charger provides.

 

My "hypothesis" is more of a general "food for thought" comment. Three things dominate battery life for all types of batteries: environment, age, and cycles. As a general rule of thumb partial cycles are cumulative. I.e. five 10% cycles equals one 50% cycle (for a FLA battery cycles below 50% discharge take more life than cycles above 50%). So if you charge a battery from 80% charge to 100% charge daily you are are eating into the cycle life of the battery.

 

The attached chart shows that the "more advanced" CTEK device "float" charging voltage is 13.0 to 13.6 volts for both FLA and AGM. This is higher than the voltage range listed for the C8 charging system when it is in Fuel Economy Mode, which is 12.5-13.1 volts. This is consistent with the idea that while the CTEK device will take the battery to 100%, the C8 charging system in Fuel Economy Mode is not maintaining the SOC at 100%.

 

Jerry, in addition to the page from my 2021 C8 CTEK instructions already posted, I found another page with specific instructions regarding "GM LI-ION BATTERIES ONLY". Again, this is from the instructions that came with the CTEK (1090) model for my 2021 C8. So, its pre- eray.

 

That's the supposed understanding / statement by manufacturers. But as one that has ACTUALLY monitored discharging and charging a battery bank EVERY SINGLE DAY FOR 6 YEARS, I can 100% report that it is NOT TRUE. That's like saying, Five kisses equals one good XXXX. Or running a mile every day for a month is like running a marathon. During t hat research, I found that a properly discharged and recharged battery bank will maintain its 99% "newness" for apx 2 years then a gradual decline initiates. By 5 years in it may be 85-90% efficient with proper cycling. Some where in the mid to low 80s% efficient, the battery approaches EOL. if you think about it 80% of 13Vdc is 10.4.For those that think 12.6 Vdc is "normal" (LOL) 80% is 10.1. Try starting your engine with a 10Vdc battery.


Again, batteries are a chemical vs pure physical reaction. It is NOT linear! To truly attain a batterie's life cycle, the standard 20 hour rating drawn (5 amps for a 100Ah battery) for half cycle (50% discharge, 10 hours for 100AH Battery) at standard temps, will yield the battery rated life cycles. BTW, discharging at the standard rate to 100% discharge will in fact prematurely kill the battery. Any deviation will change it unpredictably to human reasonable calculations. Batteries want to be in use 100% of the time for maximum performance and life. Any deviation accumulates and affects its health - permanently in any version of a sealed lead acid. This is due to the nature of the lead plates interaction in the suspended media. With a constant discharge and recharge at designed rates, full life may be achieved, but it is not practical or realistic. The constant movement of "electrons" prevents plate build up. Static (charged or discharged) situations initiates plate build up requiring effort (equalization) to be undone. This is not possible in a sealed lead acid battery regardless of what some may believe or say.

Lithium is a different story that I have not done the detail investigation on them for many reasons not to be discussed here.

With the significantly low cost (apx $150-$250) of a car battery (compared to many $$$$+ battery banks I deal with), the simplest SOP is to run it, use a CTEK charger (or equivalent) and replace it when it gets near EOL or dies. There is nothing to overthink here.

Going back to the original purpose of my initial post that some require a better title for (LOL), I noticed something that in my situation appears to be a signaling of being near EOL and I was simply asking if anyone else paid attention to their Game Changer and noticed this scenario before their battery reached EOL.

Unlike past discussions, some of these off (my topic) were interesting and I learned something new even if it was not my original purpose for this thread.

 

Since people are talking about lithium batteries, I just want to stress that the ERay's "12 V LiB may be damaged if charged to more than 14.5 volts" (GM TechLink article), so the Recondition cycle shown above should never be used (nor either of the AGM settings, obviously).

In order to reset the UVP so the battery can be charged, a charger with a "Reset" button (instead of a "Mode" button) is required. The CTEK Lithium US charger, and the 1090, both have Reset buttons. Regular lead-acid battery chargers, like the CTEK I used on my Stingray, don't.

 

"Batteries want to be in use 100% of the time for maximum performance and life."

This statement is not accurate in the general case. I am not trying to pick a fight, but I have a difficult time reading statements that are just not accurate. The FLA batteries on US submarines are very similar to what is in a Corvette. They generally last >10 years and are NOT in use 100% of the time. The one aspect that makes them different is that they are very closely monitored and have specific lifetime charging and test discharge schedules.
They are "in use" very little in the >10 years in service.

 

The part in red shows that they are in use - in essence 100% of the time. I was trying to keep it simple for most. The point is to not sit at any given SOC (state of Charge) for an extended period of time - 100%, 80%, 50%, 0%. The electrons need to move as much as possible as often as possible. I am sure that the batteries on a submarine are not sitting at an 80% or any other SOC for any extended period of time.