As far as I know, all modern vehicles have parasitic draw when not running. The vehicle systems are in low power mode, but something has to be awake to respond to remote door lock controls, remote start, and proximity sensing for the fob.

Put an ammeter on the battery cable when the vehicle is sitting and you will almost certainly see a current that decreases over time, but never goes to zero.

 

That's true...there's always some parastic draw. But I've been starting to pay close attention to this and it seems like the batteries in my vehicles all drop rather quickly (around 24 hours) to the 12.3V range, but then really won't drop any lower than that even if left unstarted for a few days. Just seems really strange. I can't figure it out.

 

If I rmember correctly from my technician days, the acceptable amp draw on a vehicle in "sleep" mode was 0.5A. That was many years ago. The standard may be different now.

 

0.5 A is huge. My "other car" will draw just under 1A for about a minute, 150 mA for 15 minutes, and 3 mA after that.
For those who don't like math, 150 mA is 0.15 A and 3 mA is 0.03 A.

 

Seeing 12.1V to 12.3V on my three cars...one sitting overnight and two for a week. Never any starting issues.

 

Yeah, same here. So strange though. No starting issues whatsoever and all the batteries still have really good amperage, but the voltage is low, which indicates a low state of charge. I never had this issue when I had cars that used regular flooded lead acid batteries.

 

What voltage do you read when the engine is running?

Do you have a reader that lets you read voltage through the OBD data?

 

It's in the 14s with the engine running. And the vehicle itself will display the voltage reading engine running or off in the off-road pages. You can also cycle through that on the dashboard display.

 

At lunch today, I went out to my Jeep and checked the voltage reading using a volt meter on the jump start lugs in the engine compartment. It was 12.21V. Then I moved the passenger seat forward and checked the voltage at the battery terminals. It was 12.15V, probably because I used the power seat motor to move the seat. I also checked the small start/stop battery and it was also 12.15V.

I noticed if I held the meter leads on the terminals for a while, the voltage reading would increase .1 volts at a time. It actually increased all the way to 12.3V before it finally stopped. This took about two minutes of holding the leads on the terminals. Again, not what I was expecting.

I'm guessing that both the big and the little battery are connected since they had the same exact voltage, but I'm not really sure about that.

I have my start/stop system turned off permanently, so im not sure if I can just replace the main battery and leave the small one alone since I never use start/stop.

 

I'm guessing that both the big and the little battery are connected since they had the same exact voltage, but I'm not really sure about that.

You are correct. The two batteries are directly connected through a relay and a fuse. The two are only disconnected when the engine is shut off at a stop.

 

Your Multimeter is not reading right. I have 5 different multimeters and 3 of them read correctly. The only 2 I really trust are made by Fluke. Get another meter and then check again. 12,1V is a dead battery. Your batteries after sitting overnight should read between 12.6-12.7V, It takes a month or more for a computerized car to run a battery down. I quite frequently leave my Honda sit for 3 months while traveling. The parasitic draw on these newer cars is almost negligent.

 

I already checked the meter and confirmed that it's accurate. 12.1V isn't dead, but it is a low state of charge for sure. Like I said, my battery tester also shows the batteries at a low state of charge, but they still have plenty of amperage to crank the engine.

 

, Go on line and look up state of charge chart for 12v batteries and you will see what the readings really mean with a digital DVOM.

 

Here you go....12.1V on an AGM is actually a higher state of charge than I expected.

 

If I know my car is not going to get any run for a couple of days or more I put it on a trickle charger.

 

I keep both my vehicles on a Deltran Battery Tender... problem solved.