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02 2.7L auto. 2 month ago the battery drained overnight. Battery tested and replaced. Now it happened again, the battery drained overnight. Nothing was left on. Key out. I thought voltage regular but then it should happen every night. Is there a common problem to check first. I am going to hook up a amp meter to the battery and see if I am getting a draw. But it has only happened twice now so I don't think I will get anywhere. Has anyone had a intermittent battery drain?
 

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""" but it might be a bad alternator."""

+1 on this
 

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Discussion Starter #4
Alternator was the first thing I thought of. But it was charging 14.2 volts on idle and 13.6 with all lights and blower etc on. I did have a truck that the voltage regulator shorted and it would drain the battery. I tested for a drain with amp meter in series and only showed .007 amps. So that's not much and so that's not the problem. I retested the alternator today after looking over the car for anything and now I only get 13.2 v and 12.5 loaded down. So it's the alternator that is not working right.
I remember when I first tested it the car was sitting overnight so it was cold. This time they had the car out and it was hot. So I can only assume that when the alternator heat up it stops working.
They had the car out the night before and had the headlight on and the a/c etc. So I am guessing that when they got home the battery was already drained because the alternator was hot and not charging. It wasnt to late and it was in town so they didn't notice the dime lights. So when they tried to start it the next morning it would not turn over. That the only thing I can think of.
So note to self. Make sure alternated is hot. I will change the alternator this week. And if it happens again that the battery goes dead I will post back.
 

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Before you replace the alternator since you said it was charging at 14vlts why not pull out the glove box light bulb and the trunk light bulb? This same thing happened to me 2 months ago and it was the glove box light. I recently replaced the fan resistor and removed the glove box. I guess I didnt put it back good enough and the switch would break contact with the lid and turn on thus draining battery. One question though...Does the car make any noises when trying to start? or any lights on when trying to start or completely dead?
 

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Sometimes oddball things like bad battery cables or connections can cause the charging circuit to be fooled and malfunction. I'd install an ammeter in series between the positive battery post and the positive battery cables clamp. You will be looking for excessive drain. Maybe 100-200 milliamps is normal, above that would be suspicious to me.
Having very clean and wire brushed battery posts and cable connections is a good start when having/diagnosing any kind of charging issue. Sometimes it's a cure. I use baking soda mixed in water and a wire battery post brush. Then rinse with water.
 

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Yeah OP's giving good advice, spend time diagnosing before throwing money at it , Hyundai alternators are pretty robust IMO.
 

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Sometimes oddball things like bad battery cables or connections can cause the charging circuit to be fooled and malfunction. I'd install an ammeter in series between the positive battery post and the positive battery cables clamp. You will be looking for excessive drain. Maybe 100-200 milliamps is normal, above that would be suspicious to me.
Having very clean and wire brushed battery posts and cable connections is a good start when having/diagnosing any kind of charging issue. Sometimes it's a cure. I use baking soda mixed in water and a wire battery post brush. Then rinse with water.
Anything above 35ma is too much
 

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20-26mA is typical "sleep" number..

I be more concerned with parasitic draw taking toll on battery..

13.2 at idle and 12.5 loaded... you got a charging concern.. alternator should pretty well maintain charge voltage.. IF you replace the alternator, buy it at Hyundai, as they change alternator for 2003, and use slight shorter belt due to new alternator pulley change to spin it faster at idle, and alternator regulator change for charging control.. dont buy a part store alternator !!

Look at connector that bolt to alternator stud, seen a few burned up, voltage drop there...
 
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