I noticed the past two weeks driving home at night my headlights would dim briefly, most noticable braking around 30-40mph, indicative of the voltage drop TSB here (and confirmed using the forum search!): http://www.amdmaddness.com/sonata/tsb/volt...p_diagnosis.pdf

But today I got my oil changed, and they performed a battery test. It was at 144CCA with battery replacement highly recommended.

Is this due to the voltage drop issue in the TSB, or is this battery really bad? It's the original vehicle battery, so it would be about time to change this anyway (2006 at 47.5k miles), correct?

This post has been edited by frozentax: Nov 17 2009, 09:39 AM

The only way to be sure is to test it yourself - get a load tester.

Also, get a cheap digital voltmeter (like at Harborfreight). The resting voltage of a good battery should be 12.6 volts or slightly over. With the engine/alternator running, it should be 14.5 volts or better.

All that said, I changed the battery on my '06 in July on a preventive measure - Wallyworld (Walmart) has them for about 60 bucks.

If you change it yourself, be sure and transfer the fiber sleeve around the old battery to the new battery - it's a heat shield.

This post has been edited by kn5owa: Nov 17 2009, 10:40 AM

I agree with this and I would also use that new meter and run the test as outlined in that tsb.

As a general rule of thumb a standard 12 volt battery should read about 12.5 volts when not running. When it is running, it should be about 13.5 volts if fully charged or higher if mostly discharged. It is not impossible for the alternator to overcharge as well and that can cause problems. The simplest way to check is to use an inexpensive voltmeter and simply measure the voltage.

If, upon starting the vehicle the voltage has a significant drop in voltage, it is indicative that the alternator is not charging properly. The voltage should drop only about 2 volts or less upon starting the vehicle. If it drops to say 8.5 volts, then it's not charging properly, or there is a huge drag from the starting motor.

I haven't recently checked these exact voltages to be overly precise but that should give you a starting point. If you hook up the voltmeter to the battery after the engine is started and you are not charging at least 13.5 volts, you got a problem. Typically, if the battery is not charging properly, the voltage will read about 11.5 volts indicating it is not being recharged.

It is not a bad idea to occasionally check the voltage to see if everything is working as it should. Any inexpensive voltmeter can tell you whether or not you have a problem. Chances are that if the lights are dimming, you have a charging problem.

Also if you have a failing cell, a cheap hydrometer will ferret out the bad cell. Once a cell goes completely bad, the circuit is broken (like the old Christmas tree lights) and you will be unable to start the vehicle. A totally discharged battery the last time I checked cannot even be jumped and it's not a good idea anyway. They have these new "smart" cables that eliminate the possibility that the connections might be bad which could fry your alternator and that could get mighty expensive. In the "smart" cables, all the connectors are blue and go through a device to sort out the proper polarity.

In the case cited, I would imagine that the battery is simply bad but don't overlook the possibility that there are corroded terminals or other issues which sometimes occur. I had to replace the battery in my JD lawn tractor last spring which also uses a 12 volt battery and at first could start it by jumping it. As the cell went completely bad, that was no longer possible. And batteries have gotten expensive as it cost about $90 to replace. I suspect the auto batteries, are just as expensive. I've always had a preference for the Sears Diehard or the Interstate brands. Some of the others are less reliable in my view.

Thanks everyone for the thorough responses! (IMG:style_emoticons/default/thumbsup.gif) I do have a multimeter - voltage of the battery sitting was around 12.5-12.8. Started the car and voltage jumped to about 14.3-14.6. After running for a bit (with full A/C and all headlights on) it was anywhere between 13-13.6.

I tested the positive and negative battery cables as in steps 2 and 3 of the TSB and had no drops (maybe 0.01v on one terminal). Wasn't sure how to perform steps 4 and 5, as I couldn't locate the ground points or ground straps (even after research on HMAService). Well, it being dark out and the dull garage light wasn't helping. Plus, my Magnum burned out in the middle. Any pointers to locate these?

Normal CCA is 550 - since mine was 144, does this still indicate cell(s) going bad? My lights were definitling diming tonight on deceleration, so I can't rule out the issue in the TSB yet until I test those other spots.

I wouldn't ponder the abstract questions too much. Your battery is five years old. Your car is a battery hog. Go out and get a Walmart Maxlife battery, it's rated tops by Consumer Reports. It's cheap insurance.

No doubt, my concern though is if the issue outlined in the TSB is the underlying cause of this.

Your voltages look great. The dealer - assuming he is on the up and up - must have used one of the new electronic testers to determine the CCA of the battery. The 144 number is in the basement. If the number is right, it probably wouldn't even crank over in the winter. The replacement battery that I got at Walmart is rated is rated at 700 CCA.

This post has been edited by kn5owa: Nov 17 2009, 11:01 PM

Yeah, it was actually at Tires Plus and that's what the mechanic was saying - definitely take care of this before it (officially) starts getting cold here. So since the current the battery is providing is so low, does that explain headlights briefly diming as the alternator struggles to keep up and provide enough current? And this, I take it, is different than the voltage drops over faulty lines like in the TSB? Just trying to be clear to either save myself a trip to the dealer or the money on a battery.. But, as others have suggested, the battery is old regardless.

I certainly would not skimp on the battery - they are pretty cheap at Walmart - and yours is obviously due.

One more thing to be concerned about with a marginal battery, and it's pretty important.

When a battery goes bad - depending on how it goes - it can take the alternator with it - and possibly even the serpentine drive belt.

If a cell becomes shorted, for example, the alternator/voltage regulator thinks it is looking at a heavily discharged battery and goes into overtime trying to charge it. The alternator, and all the electronics in it which is quite a bit nowadays, will get hot to the touch and fry itself. Nowadays, bad batteries are probably the chief reason for alternator failure (but don't quote me on that). I have had it happen, though.

When you looking at less than $100 for a battery, or maybe $500-$600 for a battery plus alternator, the choice is pretty clear.

Got a new battery and the car cranks so much quicker and with more power.. No diming headlights either. So it was due time, obviously! So the TSB didn't apply, I guess that's good. Thanks everyone for the replies!