Car battery keeps draining?!

Hey guys. I recently bought a 2019 Jeep Compass last month and was having issues with it. I took it to the shop and they replaced the battery last Tuesday (10/11) so the battery is completely new. Over the past week the digital voltage reader has started to read the voltage lower and lower each day. Just this morning it read 13.1 V and would go up to 14.0V when braking. It now currently reads 12.9V just two hours later.
The dealership can’t even get me in to check it out because they’re booked till the end of November. I took it to AutoZone about an hour ago and they tested the battery, alternator, and starting system and all are in good condition.
What could be going wrong? Could it be the battery voltage sensor? Or something else?

If you have ANY aftermarket add-ons, I’d suspect one of those is causing a parasitic drain on the battery. That is, an electronic device is staying “awake” after the key is off and draining far more from the battery than it should. All cars have some small amount of current being drawn from the battery when off. The total draw should be less than 50 milliamps (0.050 amps) when off and let sit for a while.

These kinds of devices are; aftermarket remote starters, alarms, dash cams, replacement radios and amps. If ANY of these are installed, unplug or pull their fuses and test it overnight.

If you don’t have any of those, or pulling fuses doesn’t work, you need a parasitic draw test done. YouTubers Humble Mechanic and Eric The Car Guy have good videos on how to do that test.


I don’t have any aftermarket add-ons on it and I never have anything plugged in while I’m not running it. The car was a lease vehicle prior to me owning which, I believe, would mean no alterations could be made to it.

Thank you for the advice on the parasitic draw test. I will have to try that out.

The guy at AutoZone said it could be something loose from them working on the car. Does that sound like a possibility to you?

The guy at AutoZone is not a mechanic… Loose is not likely your problem.


Your vehicle is equipped with a battery current sensor.


This informs ECU/BCM the state of charge of the battery.

The ECU/BCM then adjusts the output of the alternator to meet the electrical demands of the vehicle.

So what you’re seeing is normal.



How long/far/often do you drive the Jeep?

Sometimes frequent short trips don’t allow the battery to fully “recharge” from the alternator.

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Just to clarify…

Is your car needing a jump in the morning to start?

Or are you looking at the voltage gauge in the car and convincing yourself something is wrong?


Those battery readings don’t seem particularly abnormal. They’d be abnormal for my 50 year old Ford truck; but on a 2019 Jeep, well, the battery/alternator designs have changed a lot , especially in the past 20 years. Are you experiencing any battery related symptoms, like the engine sometimes won’t crank with the key in “start”? If no actual symptoms, suggest to simply accept this is the way your Jeep works is all.

My own diy’er basic volt-meter-based battery/alternator test is: Before first start of the day the battery should measure about 12.6 volts; then immediately after starting the engine, 13.5 to 15.5 volts. If still curious about your Jeep, you could ask your shop to perform this test & then report the result here.

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That’s part of his problem, he can’t get in until the end of next month.

But like everyone else here, I don’t think there is a problem.


In Ray’s most recent column he advises folks to avoid this problem by holding on to their older cars. Me, I’m on that idea like white on rice … lol …


Ding, Ding, Ding, We have a winner !!


I’ve never had this new of a car and being able to read the voltage on my car may be causing for unnecessary worry, but I’ve always been under the impression that the voltage shouldn’t fluctuate that much.
I haven’t had to jump it since getting the battery replaced.

No need for rudeness. I’ve had nothing but problems with car batteries in the past so excuse me for trying to nip any possible issue in the bud.

I usually drive no more than a few miles per trip maybe a couple of times a day so it likely doesn’t have enough time to completely recharge, like you said.

Thank you for your help. I’m not used to having such a new car so I’m just trying to make sure everything is fine before a huge issue arises. I’ll keep an eye on things but nothing else seems out of the normal.

Rudeness? I may have been a bit enthusiastic. But all I did was agree with someone else’s idea. I exercised restraint when I never even brought up that you didn’t ever give a battery voltage with the engine off, and that all you readings were above battery voltage, so there was no way it was discharging.
Here’s rude.
How can you say the the car keeps draining when you have no evidence that supports that? Do you even know what to measure, or how to do it?

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