In reading some of recent and past post I see that some people are having electrical gremlins and some are due to low battery voltage, once they connect to battery tender all is back to normal, my question is, does anyone
know how long can the C8 sit ( days ) before the battery starts to show low voltage ??

Robert

 

I know I put a charger on my C-7 if it sat for more than two weeks. I assume the
c-8 will be similar. There is a normal drain on the battery when it is simply just sitting there. Computer memories, theft protection, etc. all have a drain on the battery.

 

It has alot to do with the ambient temperature in which the car sits. If it's extremely cold, like below zero, it could be a matter of days before you have battery issues. In a warm garage, probably 2 or 3 weeks. To me it just makes good sense to plug in the tender when it's going to sit. It only takes about 10 seconds. I plug it in, in the garage, every time I shut it down. I've done that with every modern Corvette I have owned and avoided battery discharge issues.

 

If a car is not going to be driven at least once a week, I would probably have it on a tender.

 

Many posts on this subject. With the "new" alternator programming, the battery is more often than not at 12.5 Vdc when you park it. I plug it in as much as possible now - this is against my normal SOP, but it is required here.

 

I was able to leave my C7 sit for 3-4 weeks at a time while we were travelling internationally. Never on a battery maintainer and never a problem. The C8 uses the same battery saving technology (auto shutdown of things left on accidentally, etc.) so I expect the C8 would be similar. I haven't let it sit that long yet though.

 

There's no hard and fast number. 30 days is tempting fate. You would be wise to plug in a tender no longer than 2 weeks after shutdown. There is a steady parasitic electrical draw on these vehicles.

 

Yep, no doubt the same as my C7s! Changed my September 2013 built C7 battery after ~3 years to a AGM battery. After investigating believe it was because it probably had a weak cell from day 1.

The pic below is data from the C7 Service Manual shows with a battery in good condition you should be able to go 30 days and still start the car. In fact even with my weak battery I went on vacation for 2 1/2 weeks and never connected my battery charger. Some reported 4+ weeks sitting idle was no problem.

The problem is folks who drive very little! It takes a drive of .50 miles or more several times a week to keep it charged. A few trips 5 miles to the store drains more starting that the alienator can possible recharge!

 

From our friends over at Battery University.
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I've read 8 days for the C8, although not in the owner's manual. Unless I know I'm driving it in two or three days, I plug it in as I do my C6 and Silverado. Got tired of replacing batteries in 12 months (warranty or not). Problem solved.

 

FWIW, here is some data to offset “subjective opinions!”

Because I had issues with my two C4’s (yep leave an interior light on at night and the battery is dead in the morning) Not so foolish to do that as the interior lights stayed on for a short time. You were inside the house by then, didn’t recall you turned them on with a switch to find something. Do that a few times a conventional wet cell battery dies! Replace them, talk about hard to change batteries . in the C4 have to remove part of the fender and slide it our sideways!

When I “designed and built” my street rod bought a high, 125 amp alienator. Used a Red Top Optima battery. Initially always made sure I drove ~20 miles at least once a week (to be sure the oil was hot in the 8.2 Liter BB and “charge the battery.”) Battery died. PIA in a street rod where it’s inside the car that has electric doors! Since I wired the car myself said, "no way" the parasitic loses can be that high. Put an amp meter in the circuit and it was close to 70 ma (0.07 amps and at 12 volts = 0.84 Watts! Compare that with the smallest light bulb in your home- insignificant. However did the calculations and starting once a week that 8.2 Liter BB took time to start. That 850 Holley is not like fuel injection! When just cruising that 125 amp alternator was far from charging with the starting power lost! In 20 minutes is just not long enough

The C7 and C8 monitor current and shut down most power in ~10 minutes and all significant power in 30, as the Service Manual says.. Measured the “parasitic loses.” I measured about 30 ma. That is 0.030 amps or at 12 volts = 0.36 Watts!

However it is was my DD as was my 2017 Grand Sport and my current C8. Retired so don’t drive everyday AND may be a week if it’s raining. Rather have the wife’s SUV washed so use it! I very seldom use the equivalent to the GM battery charger. It’s an unnecessary PIA! As mentioned went on 2 ½ week vacation most summers and never plugged the charger in. (lots of lightning storms in Eastern SC and won’t take the risk and it’s unnecessary. Sold my 2017 Grand Sport after 3 ½ years, battery voltage (after the surface charge was depleated0 read fine!

 

If it's going to sit over a week I put it on my maintainer.

 

IMO, from experience and that of others, IF when you drive it's long enough and the battery is fully charged no need to put on a charger. My estimate of >50 miles at least three a week-is based on my round trip miles to town and the minimum I drive the Vette. That has worked since September 2013 when I got my 1st C7. The Vette is my only car other than the wife's SUV and now only drive the street rod to car shows. I do not use my GM equivalent charger. That has been when on vacation for 2 1/2 weeks each year. Some members report parking at an airport for even 4+ weeks.

However my experience with my street rod may also be of interest to those who find putting the car in is not a PIA. After that 1st Optima Red Top failed for what I finally measured power use and lack of charging time in ~20 mile drives two times per week, I replaced it with a Yellow Top Optima. Thankful for the warranty that covered the replacement even though it was not the battery failure, rather mine! Last year I replaced the Yellow Top- my 2nd in it's 21 years after ~9+ years. It was operating fine BUT with the battery inside the sedan and electric doors only operated with a remote- IF it failed at a car show would be a PIA! I do have a somewhat complex way to open a door if in the garage rather than break a window! However since that first six months of operation it has been on a charger 24/7. No question it has helped the battery life! But since I did all the wiring IF a lighting storm burns something out- I can fix it! In the C8 no way!

 

Let me add, driving 50 miles at a time is not typical for my trips; and replacing a battery, in-warranty or not, at the most inopportune times is a PIA. I wouldn't be concerned if my C8 was a daily driver, but it's not. The OP will need to decide based on their driving frequency and mileage per trip.

 

I've been preaching that for years!. However, that is for battery banks costing in excess of $2K-$5K. For the convenience on a vehicle, I'd bite the shortened life expectancy for the convenience. The happy medium is to not leave the charger on 24/7, but intermittent overnight - once a week at a minimum.

 

My 2011 C6 GS died after 2 weeks of not starting it in a heated garage in the winter. Never had the problem after I used a battery tender. I just recently sold it when I got my C8, and the battery always worked all summer long without the tender on it.

 

Yep, for those who drive their Vette on only short trips where it's not convenient to always use a charger, I would monitor the battery voltage. That is how I saw my 2014 battery voltage reading reading getting constantly low. Have to measure after a long drive when it's fully charged. Then ~ 24 hours after it's shut off to remove what is called a surface charge. That is a good indicator as to when a battery replacement is logical. NOT when forced to change as you say at an inopportune time.

Getting to the C8 battery is not as bad as the C7 but it has a similar concern. In the C7, although not in the Owner's Manual or 4 volume Service Manual, I always removed the lower clips on the passenger side plastic rear wheel well cover to avoid ripping the unbound carpet under that area. There were posts where dealer techs ripped the rather flimsy carpet. Not hard. For sure those that use AAA- that person when they come to jump start etc will rip the carpet IF you don't pop the bottom clips off the plastic rear wheel well cover.

The C8 has something similar from comments by a number of posters. Good chance the AAA Tech may break a clip on one of the plastic side covers! Several members report doing that. One even commented when I suggested in my Tower Cover install to only use their fingers not the recommended trim tool. They said they cracked clips even when using their fingers! Even though I only use my fingers and pull to the car center NEVER up, I used an idea posted by C8J. I put used a silicone greased on all the clips. Makes insertion and removal easier.

Suggest all C9 owner's remove the 3 plastic panels required to access the battery when there is plenty of time and not rushed. Just do it carefully!

 

My C7 battery died 5 years and 3 months.... I'm an idiot for not changing it.... learning experience.... however, you can buy a battery tender for about $90.... just plug it into a 12V outlet in the car.... EZ PZ.... but at about 3 years, just replace it... $140.... save the agro...

 

I started using battery tenders over 15 years ago on all my vehicles I stored over the winter, my garden tractor, van, motorcycles, and sports cars (several of them). Before that I would have to replace batteries every 2-3 years. Since then most still have the original batteries (some are over 10 years old) with no problems. I live in Norther Illinois and they are on the tenders on average 5 months every winter with no problems. My 2011 C6 GS I forgot to put on a tender the first winter and the battery was dead in 2 weeks. I put it on the tender and just sold it when I picked up my 2021 C8 and it never had a problem after that and still had the factory battery 10 years later. I love battery tenders.

 

^^^^ I have to agree with dragnz90, I have used them for years in South Florida (no real winter) and my batteries have lasted a long time. Was also told by a Service Advisor to always lock the car when it is being stored. He said that it puts the electronics in “sleep” mode and helps from draining the battery.