Yes, a lot lower !

 

The reality is that batteries (otherwise "identical") can be all over the ballpark regarding longevity. I've bought a couple new, name-brand batteries lately that were bad out of the box, having to be returned. And on and on, but I'll not belabor it further here. All the best, in any event.

 

A rule of thumb for as long as I can remember, learned in auto shop, a lead acid battery can lose 1/2% to 1% charge a day just sitting on a shelf.
Since the advent of AGM batteries, I have noticed longer charge retention and longer life in all my power sport stuff. My 21 Silverado has auto stop/start and it has an AGM battery in it as part of a more robust starting system , would be nice if GM spec'd the Vette with an AGM, seeing how long most of the sit.

 

OP, a couple of questions. You say "battery tender" and "meter." To my knowledge, none of the Battery Tender brand float chargers have any meter at all. Exactly what charger are you using? If it's a CTEK, and you're referring to the LEDs as a "meter," know that that's not what the LEDs indicate. The LEDs on a CTEK indicate the phase of the cycles the unit goes through, which is unrelated to state of charge.

Our own Andybump has tested the battery drain after the car is shut off and the 10 minute RAP times out. It's very low, even below GM's published standards. If your battery has really lost 60% of its charge with the usage you describe, I suspect a bad battery.

Where is this documented? I've only seen this recommended for the E-Ray. There's nothing in my 2021 owners manual suggesting this. My Stingray sat for 3 weeks with no charger attached and it started up as if it had been driven the day before.

 

I have posted the GM criteria for "charging the battery" but has more info than folks want to see or understand. Post that info about "MY trips to town and back" as some think there is something wrong when they see that stepped change in voltage from 14.5 to 15 down to 13 to 13.5 on the dash reading. It's because there is no longer a simple "voltage regulator" setting generator/alternator output it's a computer.

Same reason you see a step change in oil pressure and some low readings, all to save energy and both "computer controlled."

 

If folks think the DIC displays battery voltage, that is because the Owner's Manual tell them that. And, it may well be measured at, or near the battery. Ampng other things, the Battery Monitor Module monitor "system voltage". The connections it has can be seen in the attached schematic. It is connected directly to the negative battery post, and the negative cable is connected to the battery monitor module. Also it has a B+ (which is a connection to positive system voltage, through a 5 amp fuse to the Instrument Panel Wiring Harness Junction Box. That in turn is connect to the Battery Distribution Engine compartment Fuse Block to a 100 amp fuse to the positive post of the battery. I could not find any explicit statement that says its measurement is the one used for the DIC voltage, but if it is, its going to be pretty close to the voltage across the battery posts.

Of course if the engine is running the system voltage and battery voltage are going to be very close to the charging voltage. Not to be confused with the so called "open circuit" battery voltage that should be measured with no current in or out of the battery. And, if you want to estimate the battery state of charge using a voltmeter, that needs to be the open circuit battery voltage measured after waiting several hours for the surface charge to decay.

I do not know if that can be accurately done with the DIC meter, even if one waits several hours and does not start the car, but rather puts it in service mode. The problem, I think, is that when the car wakes up, even without starting, the draw (I measured) after waking up the car then turning it off was still 10-11 amps (not ma). That drops in steps to 10 ma after 12 minutes with the ignition off but it will not drop like that if the ignition is in the service mode.

 

Question for you all, how close are you keeping the key fob and will that drain your battery faster if it's in constant communication with your car?

 

Key fobs are supposed to go to sleep if they are undisturbed for a while. This is in the Owner's Manual. It does not explicitly say that it prevents communication with the car, but from the description is sound like that is exactly what it does.

 

My key is within ~20 feet from my Vette, BMW is ~10 feet. Replaced my C8 key at 3 years. Battery was reading low in Green OK band with an old analogy meter that loads batteries for typical use. It's selectable for batteries from 3 volts to 22.5 volts.

Of interest my BMW X5 SUV is 2 1/2 years old and my FOB had a dash display of "Weak Battery." My wife had some difficulty opening the locked door so changed hers as well. Both wee reading low in the Green OK band BUT the new batteries where at the top of the green OK band. Smart to charge at 2 to 3 years!

Also caution buying from Amazon! May be OK but had a 3 Volt battery I bought last year for my Street Rod Remote had two others in the package. One read in the Red, Weak Zone, the other showed hardly any voltage. Never know what are legit or bootlegged.

 

I haven't changed the battery on either of my FOBs - FYI, it's one of the first Game Changers manufactured. Never buy first year

 

As mentioned, the fob goes to sleep. At Spring Mountain they have you put your fob in the cup holder when you get out of the car. Sometimes you have to shake the fob to wake it up when you get back in.

 

I am not sure how long my C7 would sit without draining the battery down past the safe level, but I keep the car on a tender when not being driven. That way I know it is ready to go when I am.

 

Nothing wrong with doing that. If it's not your DD then no big deal if say you don't even drive once a week. The extra effort will get you somewhat longer battery life.

But for me, it's my DD I use and like to use to make minimum ~60 mile round trips to town ~3 times a week on back fun roads. I don't want to mess with my CKET charger.

BUT C8 owner's should understand you can let it sit 4+ weeks without plugging it in. Starting with the C7 Corvettes have circuits to shut off all significant power after ~10 minutes. Andy Bump measured a parasitic current draw after 10 minutes of ~15 milliamps. 12 volts X 0.015 amps = about 0.2 Watts. To put in perspective: According to the Journal Environmental Science & Technology, the average iPhone charger has a standby power consumption of 0.26 wattswhen not in use, consuming up to 2.24 watts charging. So yep, that cell phone charger you have plugged into the wall when not in use is consuming more power than your C8 when parked for more than 10 minutes!

 

A Battery Tender is $60 - a new battery is $200 (+/-)… Put it on a Tender, which will increase the life of your battery, and your Vette will always be ready to go when you need it to be...

 

^^^
My C8 is always ready when I need it, even after being parked no battery charger for 3 weeks when on vacation! The Corvette is better than most cars! If a DD why waste my time messing with a plug going and coming for a one year longer life?

Do folks do that for all their DD's. Heck the wife's new BMW does not have the C8 circuits that keep parasitic current draw of ~15 milliamps, (0.2 Watts of power!) If you have a garage queen fine. It you only drive once a week fine BUT the C8 parasitic current draw is better than most cars, why single it out! Believe some think it's like a Corvette of the past. The C7 and C8 are NOT!

I look at batteries like tires, always change earlier than many to get best hydroplaning performance. One incident not worth postponing expenditure for new tires.

Feel the same with batteries that have variable life depending on many things including manufacturing variations. I'll change a battery just before winter when voltage measurements say it's getting low. Saving a few dollars is not worth a PIA incident of no start in winter!