Fantastic content. I wish he had better production capabilities his work is worthy of it. You learn alot about diagnosing actual electrical issues across a variety of mfrs and all kinds of issues.

 

Probably best to just go ahead and put in a new battery - four, maybe five years is about the lifespan for a battery anymore.

 

This is an interesting approach, and I think it might work.

Once the headlights have been extinguished, the current drawn by the still-excited electrical system will be significant for several minutes - you will have to allow for that when looking for the battery voltage to increase when the lights are shut off.

With older cars, without so much electronics, and with the ignition off, the only current draw would be the incandescent head and tail light bulbs, which would be a significant current draw. I have not measured it, but a typical incandescent bulb might draw 4-5 amps, and multiple bulbs would be lit, maybe 20 amps or so? With the C8 if the car has been off for hours undisturbed, and then I approach the car with my key, open and shut the door, then wait for the exterior lights to turn off, I measure 10+ amps.

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

This is with ignition off (never turned on) and with all exterior lights off. After about 90 seconds it tapers to just under 1 amp, but takes 10-12 minutes to drop to the minimum parasitic draw of around 10 ma. I also did not measure current drawn with the C8 with headlights on - LED bulbs might generally draw less for the same lumens, but there is a lot going on in the LED headlight assemblies - I'm not sure their current draw would be lower.

So, yes, just with ignition system awakened by opening the door with key in hand (and maybe without the key I did not test that case), its already 10 amps, and with the headlights on that probably another 10-20 amps, so the draw might be as much as 20-30 amps. Which is a way to "test" the battery under load, I suppose. My point though, is that when you shut the lights off, and close the door, you will still be drawing 10 amps or more for several minutes, so the battery voltage may not come up as quickly as one might otherwise expect.

Allow for that with this test method.

 

There are plenty of failure modes that can kill a five year old flooded lead acid battery. Internal shorts are my favorite as they can make a battery short out very quickly and on rare occasion they even blow up the case spraying battery acid all over the area. Even dirt on the battery case can cause a path to ground so keeping the battery clean is critical as well.

Just remember that COSTCO sells the INTERSTATE FLA and AGM Batteries for great prices. I bought one in October that was made in September of the same year, that is a fresh battery.

IF you want to keep your battery near full charge 99% of the time then buy a 10-15 watt solar Photovoltaic panel and mount it on your body and connect it to your battery allowing the battery to get a charge.

Remember to always charge the new battery up before putting it into the Corvette, this is critical on new batteries especially.

 

Keep in mind that the charging system in the C8, and many other modern cars, targets an 80% state of charge, not 100%. The Service Manual states this.

"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 15A and greater than 8A, and the battery state-of-charge is greater than or equal
to 80%. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5-13.1V. When fuel
economy mode is active, the generator is not charging, only maintaining open circuit battery voltage."

So, even if/when the battery is charged to 100% by an external charger or maintainer, when the car is being operated it is going to allow the battery to gradually discharge back to 80%. When you park it, and attach the maintainer, it charges back up to 100%. Its been pointed out that "cycles" contributes to shortening of battery life. And swinging between 80% and 100% is a cycle. So if you drive every day, you don't need a maintainer and possibly the use of a maintainer is detrimental (maybe). GM recommends using a maintainer if you are not driving for a week or more. I will go several days or more without driving my 2021 C8, so I keep it on the maintainer every time I park it in my garage. I still have the original battery, with no issues, but I plan to change it this year (5 years old).

There is also a step for "calibrating" the battery monitor system in the car when a battery is replaced. I do not think it is critical because it happens anyway eventually. The car monitor battery voltage and also current into and out of the battery. When the car has been off for at least 4 hours or more, it measure the voltage and uses that to "estimate" the SOC of the battery. When the car runs, it then measures voltage and current in and out of the battery to keep a running estimate of the SOC. It uses that estimate to select the charging mode and voltages. When you charge the battery through the charging port in the frunk, the monitor can measure that as well. But if you charge the battery directly at the battery terminals, or replace the battery, the monitor system looses track of the SOC estimate. The calibration step is simple - just shut off the car and leave it alone for 4 or more hours. No one ever reports any issues from ignoring this - and it eventually happens anyway. So, I do not think this a critical item.

 

As I noted previously my original 2020 battery was recently showing signs of being towards the end of its life. I tested it after fully charging it and letting it rest overnight with a resting voltage of 12.6v. I used both an old fashioned load tester and an internal resistance tester. The resistance tester showed 5 milliohms and 50% life which isn't that bad. The load tester showed barely in the green but bordering on weak. I probably could have run it longer but decided I might as well change it since it was giving me warning signs.

 

How do you read the resting voltage?

 

The internal resistance tester has a digital voltage readout (the battery needs to be disconnected to get a meaningful internal resistance reading).

 

I used an ammeter to measure current and battery voltage under a load. I then measured the no load battery voltage. I sent the data to Google. Google came back with the E = IR equations that indicated my battery had an internal resistance of 51 milliohms. Google indicated this resistance indicated a defective battery. I replaced it. Happiness ensued.
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Once you allow a lead acid battery to go dead; i.e. like 0 volts, you supposedly have degraded the battery permanently roughly 1/3, if not worse. This degradation occurs even if the battery is brand new.