Does the car go into battery “sleep.” Ie shuts down everything or is the battery monitor even required if stored for just 3 weeks. Thanks

 

There is a constant drain on the battery...make sure to use a tender...

 

It should last 3 weeks without issue(assuming regular use where the car is able to charge up the battery to its programmed 80% level). There is always a draw, but the car does enter sleep mode where the draw is minimal.

Having said that, if able to, hook up a tender. Mine is always on a tender when not driven. They make it easy with the outlet in the frunk, so why not since it isn't my daily.

 

I plug mine in to the tender if I think it will sit for more than a week or two.

 

Three weeks is probably the limit if fully charged. A tender is always a good idea in my experience and opinion. A Ctek is under $100....

 

My 2021 is parked where there is no power outlet so no tender. 3 weeks sitting is no problem and I believe the most has been 4 weeks sitting. When longer than 2 months I disconnect battery.

 

Mine has set 4 weeks or a tad longer several times, no tender, no issues.

 

I’m new to corvette and new to having an “extra” car. I’ve ordered the battery tender so I have that covered. When do tires developing flat spots become an issue? Let’s say I plan on parking it all winter. Do I start it once a month and just drive around the block once?

 

Once the car is asleep for the winter, it's best to let it sleep unless you can drive it at least for 30 minutes to an hour to let everything get to operating temperature to burn off fuel and condensation.

Flat spots are not much of an issue on modern tires. Even if they develop, the first 3-5 miles of driving should get of them. IF you are still concerned, there are flat spot preventers you can buy that you can park the car on.

 

Good to know! Thanks

 

I measured the parasitic draw - on the order of 10 ma.
https://www.corvetteforum.com/forums...e-battery.html

Most of the time the car will start after sitting 3-4 weeks, but that does not mean the battery is strong. GM recommends using the maintainer if not driving for more than a week. Mine is on the charger all the time when parked in the garage.

The battery is maintained at about 80% SOC by the charging system. So it decays from that point. For two reasons. One is the 10 ma draw, which is pretty low. The other is that the lead acid battery does loose charge. After 4 weeks the SOC of the battery will be somewhere below 80%.

 

My summer toys are stored all winter....and my winter toys are stored all summer....I always use a smart charger......as for flat spots on the tires, drive it about 150mph for a few minutes and that should take care of that....

 

I can tell you last winter I used a battery tender all winter. I started the car like once a week but too snowy to drive. Battery was DEAD in March. AI says just starting the car and not driving it for a substantial ride actually killed the battery since starting draws lots current and wasn’t recharged enough by not driving. Next winter I will either just use tender and not start it or remove the battery

 

Sometimes I think AI stands for Always Incorrect! Its useful for identifying sources, but too frequently when I check the source, it turns out AI misinterpreted the info or fabricated it. Anyway, as you now know, you should keep it on the battery maintainer and you should not be starting it unless you intend to drive it. The incorrect part is that starting it "killed" the battery. Sounds like you started it once a week, and in between the maintainer was on for a week. The Corvette CTEK charger is 4.3 amps. The manual gives times to charge what it calls an "empty" battery (it does not say what "empty means) to 80%. For a 110 amp hour battery its 26 hours. Starting the car does not "empty" the battery, and a week on the maintainer if far longer than 26 hours. If everything is working right your battery should be fully charged in a day after a crank event.

So, it would seem likely that something else killed your battery. Either an issue with the battery, or the maintainer was not working for some reason, or a parasitic draw (like a Lojac).

Some believe that maintainers kill the battery. I don't. I have four cars that are on maintainer all the time they are in my garage, inside heated, and the batteries last a long long time. And I also have several other vehicles on a maintainer and their batteries also last a long long time.

Some also say that cycling the battery is what shortens it life. A cycle being a discharge then charge event. That I think can be true, but I'm not sure how much it shortens the life. The battery maintainer charges the battery up to 100%. A single start event will discharge it some, but not down to 80%. And then the maintainer brings it back to 100%. So its a "mini-cycle", and no different than if you had started the car and then driven off. In fact, the charging system in the car targets 80% not 100%, so driving it after being on the charger is going to allow the battery to "discharge" to 80%. Even so, if you start it once a week for 4 months of storage, that's about 16 mini-cycles. Hardly enough to kill a good battery.

 

All vehicles now, even my motorcycles have a constant drain. I don’t put a tender on it unless it’s a while.. At least two weeks.

 

Hi,Well, for now I have to respectfully disagree with you. I have the Corvette approved battery, tender, and use that all winter. There’s no parasitic draw on the car as I had it tested. The battery was less than a year old. The only explanation is when you start the car there’s an incredible draw on the battery and I don’t think that draw gets fully recharged unless you drive it for a period of time even with the battery tender on it

guess I’ll find out next winter 😊

 

Wait....what? You disagree that there is a parasitic draw? There is a normal parasitic draw and its on the order of 10 ma. I measured it and reported it here:
https://www.corvetteforum.com/forums...e-battery.html

I don't dispute that you had it tested - but the test procedure allows for the fact there is a normal level of parasitic draw. If a dealer tests it, they are looking for an abnormally high draw - which does happen for various reasons, such as an aftermarket device or a defective component (both are examples of what has been reported on the forum).

As for charging up after starting - again - when the car is running and driving, the charging system in the car does NOT charge the battery to 100% - that's a fact in the Service Manual, where it describes the charging system modes:

"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 A and greater than -8 A, 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 - 13.1 V. When fuel economy mode is active, the generator is not charging, only maintaining open circuit battery voltage. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present."

On the other hand, the maintainer does charge the battery to 100%. When you start the car, sure, it draws a lot of current, but its for a very short time and is not going to take the battery instantly from 100% to 80%. When you do start the car, it does enter a "start mode" which "sets a targeted generator output voltage of 14.5 V for 30 s.". After 30 seconds if it assesses the battery SOC to be 80% or greater its just going to enter the fuel economy charge mode that targets an 80% state of charge. The 4.3 amp maintainer is going to take it back to 100% shortly after you shut off the car.

A quick calculation also shows how quick it can replenish the charge lost during a crank event. Say its 200 amps for 5 seconds. How long does it take to return that energy at 4.3 amps.? ( 5 sec*200amps)/4.3 amps = 233 sec or a little less than 4 minutes, at 4.3 amps. It might take a little longer because there is some loss and the maintainer may not actually maintain the full 4.3 amps, but as I pointed out earlier, the manual for the maintainer says it takes an empty 110 ah battery fo 80 % in 26 hours. You are allowing a week for between crank events, so plenty of time to fully charge the battery.

 

Hi,Yes, the car was tested for parasitic draw
It sat overnight, the key fob was moved far away at the dealer, and the front latch was clicked so that it didn’t think the frunk was open.
It was tested at .02 amps for the parasitic draw

thanks for replying to all this and hope all is well

 

As Andy notes "with DATA" the battery drain as the OP asked "Goes To Sleep" if you check his post after ~15 minutes or less. Want to check yourself without an ammeter, open the frunk, Truck and turn on the interior Map Lights. Wait 5 to 10 minutes and watch them all turn off.

To put Andy's 10 milliamps in perspective an LED Night light, this one consumes 0.5 Watts. 10 milliamps on a 12 volts system is 0.01 x 12 volts = 0.12 Watts! Heck a single AAA penlight LED flashlight uses a much higher wattage bulb!



Here is data on the length of time a car battery can sit STARTING at 80% charge (all the alternator will typically charge to save energy.) This is from my 4 volume 2014 C7 GM Service Manual (the C7 also had battery saving circuits, but not as low a current draw as the C8. As shown with 25 milliamp current draw an 80% charged battery can sit 33 days. With 10 milliamps easily 6 weeks. BUT agree with Andy after 4 weeks I would put on a charger.



MY EXPERIENCE WITH TWO C7s STARTING WITH A 2014, TWO C8s STARTING WITH A 2020.

I have, but seldom use a GM charger. I was on vacation for 3 weeks with my C7s many times. Never installed my GM charger. Why? In SC we have many thrundertsomas in late summer days. I have replaced a number of things plugged into the garage because of lightning. NO reason to use a charger and why risk! Was on a number of 3 week vacations with the 2020 C8. Car started fine.

Now with my E-Ray and it's Li-ion battery can easily go 6 weeks. Was an a river cruise in Portugal last September and going on a 3 week cruise in Scandinavia June. Will not use a charger- NO NEED.

Your car your choice BUT NOT NEEDED.

 

Always a constant drain on the battery.