My 2002 Hyundai Sonata battery keeps draining. I have had 3 batteries: Dec 2010, January 2011, Feb. 2011; and March 2011. Now this time it drained out 7 days from the last purchase. These batteries was replaced with new batteries. The guy check my alternator and they said it was okay. Can you please give me an idea?

Over what period is the battery draining?

The alternator is likely bad. Alternators are maintainers, not chargers. The link below will allow you to easily test your alternator yourself:

https://www.askmehelpdesk.com/cars-t...ml#post1973613

Focus, particularly, on Step 9, Regulated Battery Voltage Test. If it's less than 14 volts, replace the alternator. Remember to fully charge a battery, even a new one, prior to installation.

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Originally Posted by TxGreaseMonkey

The alternator is likely bad. Alternators are maintainers, not chargers. The link below will allow you to easily test your alternator yourself:

https://www.askmehelpdesk.com/cars-t...ml#post1973613

Focus, particularly, on Step 9, Regulated Battery Voltage Test. If it's less than 14 volts, replace the alternator. Remember to fully charge a battery, even a new one, prior to installation.

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The OP said he had the alternator tested already. Also I don't agree with the link you posted. Anything over 13.2 volts is considered charging. Im not sure where the other numbers came from. 2.2 volts per cell is considered fully charged.

The best way to proceed if it happens over a period is to see what the draw is with the engine off. A small amount can go a long way.

Jwhite, sounds like something is grounded, have you had any electrical work performed, like new cd player or amp?

Cdof3, I've seen many times what passes for alternator testing at auto parts stores--it often leaves a lot to be desired. Having rebuilt many domestic and import alternators over the years, I bet the voltage regulator/brushes are bad. FYI, 14 to 15 volts is pretty much the standard regulated voltage for all alternators. Check it out.

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Originally Posted by TxGreaseMonkey

cdof3, I've seen many times what passes for alternator testing at auto parts stores--it often leaves alot to be desired. Having rebuilt many domestic and import alternators over the years, I bet the voltage regulator/brushes are bad. FYI, 14 to 15 volts is pretty much the standard regulated voltage for all alternators. Check it out.

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What we need to find out is when this is happening. If it's a sudden occurrence or if its after it sits. The alternator can be charging fine and it still be the alternator bleeding voltage. But that symptom usually happens after it sits overnight. It could also be that something else is causing a draw on the system.

Since you have rebuilt them over the years then Im sure you would realize that they are a charging device based on the field connection. Depending on the start up voltage.

So we need the OP to return and let us know the conditions this is happening under.

Feast on this:

YouTube - How to Test Alternator Voltage Output (AutoUpkeep.com)

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Originally Posted by TxGreaseMonkey

Feast on this:

YouTube - How to Test Alternator Voltage Output (AutoUpkeep.com)

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And your point is? I already stated that anything over 13.2 is a "charging" state.

The point is that the alternator is suspect, if the regulated battery voltage (alternator output voltage) is not between 14 and 15 volts, not slightly over 13.2 volts.

Elaborate on this:

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Also I don't agree with the link you posted.

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Even in the video they call out for 13.8 - 14.8. And anything above 13.2 is a charging state. How long have you been a mechanic and are you A.S.E. Certified ?

My background is in mechanical/aerospace engineering. I have never worked as a professional mechanic, which means I'm obviously not A.S.E. Certified. And your background is what? Are you an A.S.E. Certified mechanic?

25 years as mechanic and ASE Certified as well as master mechanic certificates. My speciality is Electrical Systems. I mainly work with industrial and work on LPG, Gasoline, Diesel and Electric powered vehicles.

Moving on, what specifically do you object to in the link?

Here are some links that may help in the understanding of what we are talking about if anyone is interested.

Battery Basics - How a Battery Works - Voltage

Catalog

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Originally Posted by TxGreaseMonkey

Moving on, what specifically do you object to in the link?

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The "standard" for indistry has been 14.2 volts as long as I can remember as the "ideal" voltage. And as we both know that number is going to fluctuate by the amount of charge in the battery and the "load" on the system. If you were to read 15 volts at any time I myself would monitor the system for other problems. The last thing anyone ever wants to do is cook a battery. It can be an extreme hazzard.

What wasn't in the video is that anytime your going to make tests like what was shown you always need to make sure the terminal connections are clean. If not you can experience a voltage drop across the post to terminal end. And finally we both know that voltage isn't the only factor. If its not producing amps its still not doing anything. It will never charge.

Let me make this clear. As an open post. Im not trying to discredit TxGreaseMonkey. We both come from different wells of where our knowlage is drawn from. His advice is still sound. We are just sniveling in an open forum over fine points. Lol