I installed CarLock and one of the features is voltage monitoring. My battery has been consistently reading around 12.0V at rest but starts up fine. I have zero issues. Car is driven on weekends, if it sits longer I use a charger/maintainer but don't bother otherwise. Is this normal to see or could it be indicative I need a new battery soon? What threshold should I be concerned if it drops below (i.e. it may not start)?

I contacted support and they said they can manually change the minimum threshold but want to know what I want it to be set to. They have it hard coded to 12.1V and I get spammed with notifications every day about it being low despite starting just fine when I need it to. I think it would still be useful to me to know if I've gone too long without plugging the charger in or the battery is starting to have issues, so would 11.5V be a better threshold to set if this is normal?

 

I'd question if it is giving accurate voltage output. When the car is "awake" but not running there will be items drawing current which would reduce the voltage at the port. I'd measure the voltage directly at the battery or accessory outlet in the frunk. You'll need to open the frunk lid and let the car sit for at least 10 minutes (longer would probably be better) and take a voltage reading with an accurate multimeter. The voltage should be around 12.6 to 12.8 volts. It may be higher if the battery has been recently charging.

 

2021 you’ll be due for a new battery.

 

If it is accurate, and if you are reading resting voltage after the battery has sat with no (or negligible) draw for several hours, its low, yes. Mine new battery reads 12.1-12.3 on the DIC when the engine is off but the system is in service mode, drawing 10-12 amps (which is not "resting voltage"). My 5 year old battery in my 2021, before it was replaced, was reading the same thing under the same condition with the DIC. Resting voltage would be higher.

You can find different charts with slightly different numbers, but his chart is purported to be for an FLA battery, resting voltage. I don't necessarily recommend that you go entirely by resting voltage though - its subject to so many variables. I recommend having a battery load tested if an when you have a concern. I replaced mine just because it was 5 years old. Did not bother to test it. Did not base it on voltage readings.

11.5 would be terrible I think. The battery should be 80% charged after the car has been run for a while. Thats 12.4 resting voltage or thereabouts.

 

First, as others said IF the battery is only 12 volts get ready for a new one!
Possible but you can put the Car Volt Meter on the Dash. It reads alternator voltage (unless you had an E-Ray as I do, where during stop/start it reads battery voltage after a few seconds as NO alternator!)

But my MO for checking "battery Voltage" to define when it's declined and ready to consider a new one is to use a Volt meter. Today even the inexpensive ones (~$15 on Amazon; ~$7 at Harbor Freight) are solid stat, LED readout and have a very high impedance so accurate. Can check with a new 9 volt battery!

Can check directly at the battery with the car off. Need to wait for all the battery current limiting controls to be active. Just open Frunk and wait ~15 minutes. That will give a good indication of the battery voltage at rest. Best to do that after the car is NOT been driven for >12 hours so you are not reading the surface charge.

If that reading still shows 12 volt your due for a new battery. Buy now or wait until the car won't start when it may not be convenient to replace!

SIDEBAR
BTW I made a simple way to check without having to remove the Frunk plastic to get to the battery terminals. Made for my 2014 C7 using the battery charger receptacle like the one in the C8. I just cut the plug from an old 12 volt car vacuum and installed a female plug on the two wires. Put the Voltmeter probes in the female socket!


Pic of Plug with female plug connected to the two wires. BTW have checked the $7 Harbor Freight LED Volt Meter with my quality Fluke VOM. It read identically. Harbor Fright, when they still had coupons every week, gave them out FREE. I have several!
13.28 is the voltage of my E-Ray Li-Ion battery.

 

I would much rather replace the battery early own my terms than wait for the car to tell me to replace it. It may coast less in the long run.

 

CarLock is reading 11.7V, multimeter (borrowed from roommate so hopefully it's a good brand) reads 11.8V. Car hasn't been driven since Friday and is not on the maintainer. This is a few minutes after I opened the frunk; I'll come back and check on it a bit later as well but the frunk light is still on.

Something to note is I have the CarLock and two LED controllers connected to the battery. The CarLock has a small drain for GPS monitoring but the LED kits shouldn't affect anything. Would this impact the resting voltage at all?

I already have a LiOn battery in my cart recommended to me from another member that he bought back in September 2025 and reported it has worked flawlessly. If this is a sure sign the battery I have is about to die, I can order it but I do carry a jump pack with me to car meets/shows (only time the car is driven), so I think if it dies on me while I'm out I could at least make it home running off of the alternator... But if that didn't work for some reason, it would indeed suck.

 

Umm…

 

That seems too low but I'd wait until the car has had a chance to go to sleep to be sure. And I'd do the testing without the CarLock connected. It's probably time for a new battery assuming this is the original battery. You can charge it up and get it load tested to be sure. You can also charge it up, disconnect one of the terminals, let it rest for several hours, and check the voltage with the multimeter. If it is still below 12.6 volts it's time for a new battery.

 

OP, I see the Carlock device connects to and draws power from the car battery. You mentioned its draw is low. How do you know that, and what is the draw? The normal draw when the car is asleep is very low - I measured 10 ma. Also, which side of the battery monitor did you attach it?

I looked up the Carlock and found the installation procedure, but did not yet find a spec for the current draw.

 

Just checked again and it's 11.9V now. I'm going to charge it up with my Noco Genius 1 in the charging port, disconnect the charger then the negative terminal, and check with the multimeter again after disconnecting the charger for a few hours. I'll see what happens then.

The CarLock reads the voltage from the battery and displays it in the app, I'm not using a separate voltage monitor. I need to ask what the current draw is, but my statement was an assumption and based off of being able to let the car sit for a week with no charger on it and have it still start up. So not like leaving an interior light on for several days and then finding a dead battery when I go to drive it again.

 

My question about the battery monitor was not clear, sorry.

The CarLock installation instructions show connection directly to the battery posts. Is that what you did?

The car has a battery monitor that sits between the battery terminal post, and the negative battery cable. Its job it to measure all of the current into and out of the battery. And that information is used by the BCM to select the charging system modes when the car is running. If you connect an aftermarket device directly to the battery posts you are bypassing the battery monitor. Its not a big deal if the current draw is very very low--- my question was really where did you connect the negative lead of the CarLock device? Directly to the negative battery post, or on the other side of the battery monitor? Its probably not important if the draw is low but is it.

The CarLock is not just a voltmeter. Its running a GPS receiver and transmitting your location and alerts to the "carlock cloud", likely using a cell connection. That takes energy. Is it like a Lojack? If so, a Lojack draws something on the order of 40-50 ma, which is 4 to 5 times the normal parasitic draw. And, though your vehicle may start, the voltage readings you have, if accurate, indicate that your battery SOC is low. Another member was having trouble with low battery and it turned out he had an aftermarket Lojack attached. Not saying that is your issue, but its a possibility.

See this thread, in particular posts 35 and 37
https://www.corvetteforum.com/forums...-charge-2.html

 

Battery is coasting at 12.5V (per multimeter) on the charger, I'll check it out tomorrow and disconnect once it hits the green LED that indicates "maintaining" and we'll see what happens. I'm probably taking the car out Friday so I guess we'll see if there's a big voltage drop while it's disconnected? I know advance Auto parts does battery load testing but not sure how reliable that is, any other suggestions if there is somewhere better I could trust to give me a state of health on the battery?

It's a GPS tracker that polls every 30s and also has a vibration detector that has gone off when I open/close the door and forget to disable the notifications in the app. I haven't used a LoJack but this is my first tracker I've connected directly to the battery. They sell other sensors you can pair with it but I'm not using those, just the main unit and it's connected like your picture. More on that:

I put everything on the nut labeled 1 in your image, so not the one that clamps the terminal to the post. CarLock, 2 Bluetooth controllers for LEDs, and a ground for the module that does my RGB DRLs. Putting the eyelets on the other nut that controls the clamping force would be really difficult. The positive side has two nuts as well which might be for a similar reason, for this I also used the nut that doesn't control the clamping force of the terminal.

 

THIS!

It will cost less as you can shop at your leisure and buy a top of the line battery on sale (Memorial Day is usually a good time) in stead of being stuck with buying an inferior battery at list price.

 

Thanks. Connected that way you are not bypassing the battery monitor with the aftermarket connections for the devices you listed. Lojack was just for comparison purposes for guessing what current the CarLock might draw - because they publish their parasitic draw.

CTEK does not include the charging profile detail in the manual for the Corvette version, but they do include that information in the the manual for other similar CTEK maintainers. Attached is the profile info in the CTEK MXS 5.0. It shows that in the float mode, for the FLA battery, it maintains 13.0-13.6 volts. Now, I'm just pointing out what the manual says...I have not confirmed that myself by measuring the voltage at the battery with the charger connected and in the float mode. But this float mode voltage is higher than the nominal "resting voltage" which would be measure at least 4 hours after the battery has been off the charger, and no (or negligible) current is being drawn.

If a battery has been charged to 100%, then when you initially disconnect it from the charger, the voltage you are going to read is the result of what some call a surface charge. A healthy 12-volt lead-acid battery should read between 12.6V and 12.8V after resting for several hours with no load or charge input. With surface charge still present, that same battery might read 13.0V to 13.2V or higher, depending on how recently it was charged.

I feel like that's a good bit of stuff connected that adds to the parasitic draw. You could measure it if you want to, using the method I used, as reported in this thread. You would want to put the clamp meter around the positive battery cable.

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

 

You have a lot of wires coming directly off of the positive terminal of the battery. I hope for your sake that each one of the connections has an inline fuse very close to the connection at the battery. If not, you have no overload / short circuit protection. If those wires short to ground there can be a lot of damage to you car. Including a fire.

 

Hmm, the fact that the Frunk light was on after ~5 minutes would make me concerned. As Andy notes after all the battery saving circuits are started, the parasitic current draw is only 10 milliamps! That is VERY VERY low, at 12 volts that is 0.12 Watts! I find the Frunk light is off after ~5 minutes. If it is still on, the parasitic limiting current draw circuits have not all started. That can drain a battery quickly. Can find many posts where the over the air software updates prevented them from starting and the battery was dead in ~12 hours.

SIDEBAR
Just how low is C8 parasitic power??
An LED nightlight draws 0.5 Watts. The smallest incandescent night light is 4 watts. That is about the same as a TV on standby waiting for a remote to trigger it to turn on. The parasitic current draw x 12 volts with all power saving circuits fully operating is ~30 times less power consumption!.

 

Fuses? Don't need no stinking fuses...

 

Right......

 

Not a corvette…