Hi,I have a 2023 2LT Z 51. Had my car on trickle charger. All winter seemed fine. Started up a few times, but didn’t drive much in the northeast. So now we’re driving again and seemed every other day the battery is dead car won’t start. I can jump the battery with my booster and it starts right up. The battery display on my dash shows me once it’s running the voltage is perfect somewhere around 14 V. Now that the trickle charger is off, it seems the battery goes dead overnight. I’ll measure the voltage in the morning with the charger off the car see what it says but I suspect it’ll be low.So I’m suspecting over the winter when I installed a mirror tap for my radar detector. This could possibly be the issue of draining the battery. However, if I have my radar detector plugged in to the mirror tap when the car is off the radar detector goes off , when the car is on the radar detector comes on so I find it hard to believe that power is going to this mirror tap when the vehicle is off. No other changes have been made and the car certainly ran fine prior to the winter in terms of this battery issue.Anyone have a comment or similar issue?Thank you.

 

It's not your mirror tap. Confirm with a battery tester and replace it if bad before it takes out your alternator. Was your trickle charger a smart charger?

 

A battery maintainer can mask a battery problem. It will keep a marginal battery charged when on it but when you take a drive and park it for a few hours without a maintainer it doesn't have enough power to start the car. As mentioned, get the battery tested. Another test would to be to disconnect the battery and let the car sit for a couple of days. If it doesn't start in the morning after the battery was reconnected (assuming it was charged when disconnected) the battery is bad. If the car starts fine then start looking at somewhere in the car.

 

I am very convinced that continuous battery tender use will shorten battery life overall. Your battery was already at marginal life and the tending may or may not have had an influence, but I suspect it did. I will use a tender occasionally after letting it sit for a few weeks to discharge due to normal parasitic draws which vary from vehicle to vehicle. A battery that is cycling through somewhat normal charge and discharge cycles will last longer than a battery always being tended, in my experience. YMMV.

 

hi
i’m not sure what you want me to confirm the mirror tap or the battery? When I test the battery cold with my voltmeter, it reads 12.4 volts.
My trickle charger is the Corvette approved one that plugs into the drink cigarette lighter port. If I had the trickle charger on all night, the battery is fine and it starts. Once I pull the charger off overnight battery is dead basically, 12.4 volts.

 

Gee I’m using the Corvette approved charger via the frunk cigarette port…,,,
I can try your idea also & see

 

interesting since I’m using the Corvette approved battery tender. The battery itself is stamped of May 2025 not even a year old and of course I probably only have driven the car six or seven months.
if the battery tender doesn’t work correctly, and I only drive the car in good weather not the winters in the northeast. What do you suggest to do since I won’t be driving the car. Do I disconnect the battery for the winter?
I do use that identical battery charger on my BMW and it seems fine

 

Test your battery capacity with a battery load tester. Buy a tester, or take the battery to autozone, o'reillys or advanced auto parts. A DMM doesn't test the battery under load.

I have also had a car not start due to a stretched clamp that wasn't secure enough.

 

Yes you should keep a battery maintainer on a car that is being stored. What @rdbragg was talking about is daily use of a maintainer. GM recommends using a maintainer if a car isn't driven at least weekly. Also, you can't blindly trust that mainainers are working properly, some keep the battery in an overcharged state. It is OK for them to periodically go into the charge program but the battery shouldn't be constantly held over 13.6 volts.

If your battery was truly made in May of 2025 it is suspicious that it was replaced and is having problems, but it can happen. As mentioned it would be good to have it load or resistance tested but you need to let it rest for several hours after charging before testing to let the surface charge burn off to get accurate results. If you disconnect it after charging and let it sit overnight and your voltage drops to below 12.6 volts then it is probably bad.

 

You can check the parasitic draw with a low current DC clamp meter as I did, recorded at the thread below. After 10-15 minutes undisturbed the draw should be on the order of 10 ma. If you see more than that, you have something drawing current. Your dealer should be able to check that too, but I don't know if they do that or not.

But you wrote "Once I pull the charger off overnight battery is dead basically, 12.4 volts". Are you saying it still reads 12.4 volts after being of the charger overnight and unable to start the car?

Here is the link to my parasitic draw test:
https://www.corvetteforum.com/forums...e-battery.html


This is the clamp meter. After the car is shut off, the various systems shut down in stages so the current draw drops (it starts at 10 amps for a fully awake system) in steps. Its showing 300 ma here, but after a few minutes it eventually drops to 10 ma or so.

 

I am fairly certain I found the problem. I suspected the mirror tap used for my radar detector. What was strange was when I plugged in the radar detector today it basically flickered it wouldn’t stay on, but it wanted to try. This is after I got the car started. I have used that radar detector and that mirror tap several times without a problem.So I unplugged the wiring from the mirror used to radar detector from the cigarette port. I ran the car for 30 minutes shut it off started right up. Ran it another 30 minutes shut it off started right up. My hope is that this is the cause and I won’t mess around with a mirror tap anymore. I’ll really know the answer either tomorrow or the day after since I won’t put it on a trickle charger or have to use my battery booster to jump it.Thank you for your information. We’ll see how it goes.

 

pretty sure I found the problem which I suspected was the mirror tap to my radar detector. I plugged in the radar detector today with the mirror tap and it flickered a few times did not want to go on. I took the wiring off of the mirror and use a cigarette port for the radar detector and it works fine. I ran the car 30 minutes it showed 14.2 V as I ran around in town. Took it home started it right up again. Ran it another 30 minutes. The voltage was fine again. I’ll really know the answer to this after a day or two with the car off of the trickle charger and no battery booster jump.Thank you for your help.

 

If the mirror tap was tapped into the correct wires then the power will be switched off when the car is turned off. Other people have used the mirror tap to power their RDs without draining their batteries. Hopefully it is because the RD was tapped into a wire that had continuous power but it doesn't sound like it.

 

Maybe so , maybe not. If you are hooked to the correct pin, it is switched - no one has reported an issue with it. But many have reported connecting to the wrong pin - and that can be a big issue. And if it is connected to the correct pin, then flickering on and off is not good at all. Something wrong somewhere. When you say you took the wiring off the mirror, did you remove all modifications you made there.

But the 14.2 volts you read while you "ran around town" is while the engine is running right? You are reading it on the DIC aren't you? So that is charging voltage. Charging voltage will be all over the place and is not a real good indicator. A higher voltage, like 14.2 could mean the car is still in the charge mode, meaning the battery is not fully charged. When the battery reaches the target state of charge, which by the way is only 80% and not 100%, the charging system switches to fuel economy mode under most situations. In that mode, the voltage should range from 12.5-13.1 volts. Seeing 14.2 means the system is probably in a charging mode - it thinks the battery is not fully charged. There are too many variables to be sure though. This is directly from the Service Manual:


"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."

 

yes, the mirror tap was tapped into the correct wires.
When the car was on the radar detector came on when the car shut off the radar detector shut off, and I tested the wires with my motor meter also.

 

So, since all that was working properly, then why do you think it was your battery problem? And why did it flicker?

 

I did not realize that your battery had been recently replaced when I presumed your battery was at marginal life point. I put the battery tender on it every couple of weeks (or even longer span) and let it sit for about 24 hours and then take it off the tender for a few more weeks. I see you think you found the excessive drain source. Hope that was it,

 

FWIW, my new 25 Z51 1LT coupe built 5/16/25 had a little over 6,000 miles on it when I went on a 5 week vacation. Stored in an attached garage that never goes below 40* F. I decided to use the GM battery maintainer that came with the car even though I've never used one before due to all I read about the C8's electronics and others with battery issues. When I returned home I started the car up and it fired right up no problem. Great. Weather was still cold and several feet of snow so I let it sit another 2 weeks with the tender on. When things cleared up I got it out and took it for a 70+ mile drive. The next morning the car would not turn over. "Battery Low Start the Car" message as well as multiple codes and a CEL. Did the "open the door for 15 minutes" soft reset trick and to my surprise it fired right up. Took it out for a drive again soon after and everything seemed ok. Next day drove it a few miles to the store and when I came out battery was again too weak to turn the engine over, more codes and warnings. Left it overnight in a supermarket parking lot and had a friend give me a jump the next morning.

Took it to the dealer and they put it on tester GM requires them to use if they are making a warranty battery claim and sure enough the battery was bad. Replaced under warranty with a new one. Have driven 700 miles since and no issues....but...I 've been driving it regularly and like you, I'm not sure about what to do if I store it again. I've owned 19 Vettes and never used a battery maintainer of charger before and never had an issue. The one time I use it and the battery goes bad prematurely. Makes one wonder.

 

the battery was dead car wouldn’t start. I suspected bad battery since I had car like 9 months.
no idea why it flickered maybe loose connection- I removed that tap and all seems fine now - but tomorrow will tell if car starts