Question

Hyundai Sonata Battery Drain Mystery

Has anyone had a constant battery drain? I've had the car in 11 times and was finally told it was because I had an after market alternator installed. But the thought from other mechanics is that there is something running that randomly does not shut off when the car is off but can't locate what that something is. Below is what I've gone thru. Any thoughts?
8/2017: Dead battery replaced at Auto Zone
9/2017: Dead battery; was jumped but alternator and battery were testing good; “must have been a fluke”
11/17/17: Dead battery; GL Hyundai said Autozone gave me a bad battery; Autozone replaced the battery under warranty
12/27/17: Dead battery; GL Hyundai said it’s because it is not a Hyundai battery and replaced it with Hyundai battery
1/5/18: Dead battery; GL Hyundai said it was fine; teo hours later called me back and said it was the alternator & $727 to replace
1/6/18: Took to local mechanic and replaced alternator for $359
1/15/18: Dead battery; GL Hyundai replaced the battery under warranty because old alternator supposedly drained it
2/5/18: Dead battery; towed to local mechanic & said alternator is fine; must be something running that is draining the battery when the car is off; taken to GL Hyundai
2/10/18: GL Hyundai said bad alternator because it is not an OEM alternator
2/12/18: Local mechanic can warranty out current alternator for Hyundai alternator for $214 but still don't think it's the alternator

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Clarification Request
remove the trunk light

Or have someone small enough to get into the trunk while you close it to see if the light stays on. Check it several times.

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Clarification Request
there is an easy way to test

If the trunk light isn't the problem. Disconnect the battery negative cable and put a meter between it and the cable. Remove and replace one fuse at a time, checking meter each time. That way you will find what systems are drawing power when the car is turned off.

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Clarification Request
Similar issue

Purchased 2012 Sonata in Dec-18. Batt went dead 3 times in first month. Batt new oct 18, checked out fine at auto store. Tech spent 5 hrs checking every circuit. Still getting “250 mv draw” that he can’t isolate. His next suggestion is to take it to dealer. I can’t believe that seller didn’t have to jump this car when he bought it...may have bought battery if he thought that was issue.

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You need a better tech.

Actually it may take two. Why? One tech watches the Ammeter and the other removes the fuses one by one until the current drops. NOTE: YOU NEVER just pull all the fuses. You go one by one, test then put the one you pulled back in. Otherwise you lose a day trying to put the right ones back in.

Now that you know the circuit it's on, the service manual might be used unless the circuit is something easy like the trunk light.

Post was last edited on March 29, 2019 9:48 AM PDT

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Answer
This requires the tech to...

Get the car in the shop and MEASURE the current drain when the car is off. This is in the service manuals so my questions are (1) was this done and what was the reading?

My last mystery drain (it wasn't since the tech measured it) was the GPS Nav unit. It worked but drew 1.5 Amperes when off. Thankfully under warranty. No, not writing it is this in your case. Just an example where the tech measures current draws to find what it is.

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Answer
Hyundai Battery drain mystery.

Been having similar issues with my Hyundai. I think its the lights. What mode are your lights in. When I left mine in auto mode, the next day it was draining. Everything was very weak. Last night I left them in the off mode and this I didn't have an issue. I took it to Sears to check the battery. I wish that had been the problem. He checked battery, alternator and said he noticed an issue with light switch and indicated an electrical wiring issue.
I hope that helps you. I saw a similar post in another forum where they also had an issue when lights were in auto mode.

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Mystery Solved

I finally was directed to a dealer who concluded the radio had a short and the whole unit had to be replaced. After a lot of back and forth, Hyundai gave me enough points to pay for the $600 replacement. By April it was resolved and I haven't had any problems since!

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Santa Fe battery Issues

Currently having the same sort of issue with my 2012 Santa Fe. It starts with the lights dimming on and off while driving and then the battery light comes on, and basically goes through the whole scenario as if the alternator was gone. My mechanic tested it and said it was fine but has now replaced my battery twice without the issue being fixed!! So I’m curious if this is the same problem?

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Radio draining power

I've had the exact same issue with my 2011 Hyundai sonata limited. Did everything from changing battery, to checking alternator and then some. Found out there is a short in the radio and its causing the battery drain. This car has been a nightmare in recalls and had the motor replaced from a recall as well. Sounds like everything on it is messed up

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