# How can you tell if a battery that tests good, is really bad?



## Hydros

*This is for the lead acid type of batteries.*


Here is the situation; customer comes in and complains that the battery is always dead. 

The correct way to test a charging systems is to make sure the battery is fully charged and that the battery has then tested good. The battery is tested, such as load, recover and maybe even with a hydrometer and all the results are good. 

Then tests the alternator with an internal regulator and it fails the test. Alternator/regulator is replaced, and the starting charging system then tests good. All looks good and the customer is on their way.


With a few weeks the same customers come back and complains of the same problem, once again the alternator is found to be bad and is again replaced. 

Question was/is what can cause this? 


$20.00 to the first person to give the correct answer or $10.00 if they are even near the correct answer.



_question was first posted on www.squaredump.com and www.layitlow approx 7 years ago. _


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## DirtyTrixsHydros

low acid level in da battery? i would think the battery would go bad causing the alternator to over work and die?


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## CoupeDTS

For one, after working at a parts store, I learned to realize cheap reman parts go bad more than you would think. I even went through 3 alternators in 6 months in my old daily driver until i stepped up to a AC delco and never had another problem. Some remans might have new parts in them but if the regulators tested good before then the reman company might not change that certain part out, just the other parts. Reman alternators arent like reman water pumps or starters where theres only a few parts to the whole thing. Alternators have lots of electronics in them that can go bad and so they can go bad more often. Reman companies have warranties and you should use them. Its not uncommon at all to go through a few alternators before you find a good one. You may have found a crappy batch of them at the store. Switch stores or reman brands or step up to a name brand! 

All that is assuming you are using reman alts. Also you didnt say if its internal or external regulators or what kind of car it is if its modded or not. Underdrive pulleys kill alternators because they are run too low and they dont like it. 

Oh, and make sure they arent car wash finatics that wash their engine all the time. Water in a alternator isnt good. 

Theres not really anything else that affects the charging system. Grounds need to be all good, dont forget that.

Good luck.


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## Hydros

Since this forum runs so well, I will give out clues and replies of why your thoughts are valid, but not on target.


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## Hydros

DirtyTrixsHydros said:


> low acid level in da battery? i would think the battery would go bad causing the alternator to over work and die?


Yes, your reply is correct, but, in this case, the battery was correctly checked before charging, then let sit a few hours to dissipate the bubbles before the hydrometer was used. 
You are corrected the battery is bad and is causing the alternator to go bad, but why?


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## Hydros

CoupeDTS said:


> For one, after working at a parts store, I learned to realize cheap reman parts go bad more than you would think. I even went through 3 alternators in 6 months in my old daily driver until i stepped up to a AC delco and never had another problem. Some remans might have new parts in them but if the regulators tested good before then the reman company might not change that certain part out, just the other parts. Reman alternators arent like reman water pumps or starters where theres only a few parts to the whole thing. Alternators have lots of electronics in them that can go bad and so they can go bad more often. Reman companies have warranties and you should use them. Its not uncommon at all to go through a few alternators before you find a good one. You may have found a crappy batch of them at the store. Switch stores or reman brands or step up to a name brand!
> 
> All that is assuming you are using reman alts. Also you didnt say if its internal or external regulators or what kind of car it is if its modded or not. Underdrive pulleys kill alternators because they are run too low and they dont like it.
> 
> Oh, and make sure they arent car wash finatics that wash their engine all the time. Water in a alternator isnt good.
> 
> Theres not really anything else that affects the charging system. Grounds need to be all good, dont forget that.
> 
> Good luck.



CoupeDTS good to hear from you. As always, good points with details. With this scenario, the alternator does have a built in regulator and it can be ANY car. The alternator and reg are known good parts, new/rebuilt. ANY CAR WILL DO, But should have the old type of alternators that do not need to be excited to charge.


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## Hydros

SOMEWHAT CLUES:

THE analog SUN VAT 40 is the tool I used to find this. This is an outstanding tool. The VAT 60 is digital and I feel is somewhat lame in finding starter draw.

Google was not around when this question was first posted...


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## orientalmontecarlo

i know that if you weld electric on the car without disconnecting terminals it can mess up an alt. or battery..


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## orientalmontecarlo

and battery can have a short internally


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## Hydros

orientalmontecarlo said:


> and battery can have a short internally


go on...


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## biggie84

I've found bad ground will cause the same thing ground off the batterie to chassis or etc...


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## orientalmontecarlo

Hydros said:


> go on...


dendrites and sulphate form on the internal plates causing a short,if you get of rid of that dendrite by fast charging or zapping it then the vapor of the burned off dendrite itself acts as a resistor and in turn makes the battery weaker or dont hold a charge..

but...... doing that can cause more dendrite depending on the electrodes in the battery.


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## Hydros

orientalmontecarlo said:


> dendrites and sulphate form on the internal plates causing a short,if you get of rid of that dendrite by fast charging or zapping it then the vapor of the burned off dendrite itself acts as a resistor and in turn makes the battery weaker or dont hold a charge..
> 
> but...... doing that can cause more dendrite depending on the electrodes in the battery.


???? just when I thought I knew it all. Not really sure what that all means, but man it sounds good. 

OK, how do we determine what is the real cause of the charging problem? It can be found testing the charging system, but most times the tech don't know to take the extra time, to make sure all well.


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## Hydros

I will give the answer out Sunday night or Monday.

We'll just include the regulator with the alternator and call it "alternator"

Another hint, the alternator tested good each time, yet failed later. What things can cause an alternator to fail? Thinking it out, you will have the answer, just need to state how to spot the problem. 

Good luck!


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## orientalmontecarlo

Hydros said:


> ???? just when I thought I knew it all. Not really sure what that all means, but man it sounds good.
> 
> OK, how do we determine what is the real cause of the charging problem? It can be found testing the charging system, but most times the tech don't know to take the extra time, to make sure all well.


some people zap or fast charge batteries when they've left it sitting with no charge for long periods of time


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## Hydros

edmunds costoms hyd said:


> use a load tester...


Edmund! go on.... tell me more, what exactly are you looking for or looking at?

Remember all, it is found while doing a charging systems test. BUT what are you looking at that tells you something is bad?

And regarding my harem of haters, you are invited too.


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## edmunds costoms hyd

Hydros said:


> Edmund! go on.... tell me more, what exactly are you looking for or looking at?
> 
> Remember all, it is found while doing a charging systems test. BUT what are you looking at that tells you something is bad?
> 
> And regarding my harem of haters, you are invited too.




Well the load tester will --- put a load on the battery, like the same as if you were starting a car. If the battery has a bad cell , the meter will drop to bad on the reading or low numbers on a digital type. Back in the old days we were able to pop the caps off the batteries and if there was a bad cell it would smoke a little and would like boil while the other didnt.


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## edmunds costoms hyd

thats my storie and sticking to it....


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## Hydros

OK more hints, lets see...

Ok, we have charged and checked the battery. We used a good load tester like the VAT 40. then we also double checked and used a hydrometer. All looks good. 

We have replaced the alternator. Now we retest the charging system. What always happens when you check the charging system and the car is running? You check for volts and amps, and apply a load. The correct way is too turn on everything in the car, headlights, radio, flashers, heater, things like that. There should be a reserve or higher output from the alternator to overcome the load from the car. 

There is another load not mentioned, it's the electrical system the engine needs to run. The answer is in here in the underline.


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## Hydros

I'll post up more hints again. If you google it, may or may not be worth $20. 

The primary and secondary electrical systems requires what to run the engine? What are we checking/looking for when we check the charging system? As stated above, it is volts and amps. (disregard the diodes, because we installed an alternator that tested good). 

I'll give hints until someone wins. So a little after brunch I'll give out more to make it fair. - YES BRUNCH, MOTHERS DAY, DON'T FORGET.

got to set a closing date, winner or no winner, thats Tuesday 9PM, Good luck.


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## Hydros

Hydros said:


> I'll post up more hints again. If you google it, may or may not be worth $20.
> 
> The primary and secondary electrical systems requires what to run the engine? What are we checking/looking for when we check the charging system? As stated above, it is volts and amps. (disregard the diodes, because we installed an alternator that tested good).
> 
> I'll give hints until someone wins. So a little after brunch I'll give out more to make it fair. - YES BRUNCH, MOTHERS DAY, DON'T FORGET.


OK, hint time, when the electrical systems running the engine uses amps and volts, it causes a ______ on the ____________ .


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## Hydros

Hydros said:


> OK, hint time, when the electrical systems running the engine uses amps and volts, it causes a ______ on the ____________ .


OK, hint time, when the electrical systems running the engine uses amps and volts, it causes a load on the alternator. 

So, can we _________ this load? yes, because we doing what?


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## Hydros

Hydros said:


> OK, hint time, when the electrical systems running the engine uses amps and volts, it causes a load on the alternator.
> 
> So, can we _________ this load? yes, because we doing what?


So, can we measure this load? yes, because we doing what? We are testing the charging systems and can see what is going on with it. 

So, what is the average load on the alternator when it supplies power to the ignition system?

Now when you install a perceived known good battery, and it's not fully charged, but charged good enough for testing the charging systems, what happens to the amp and volt readings after a few seconds/minutes? The volt readings go up and the amp readings come down. 

So the tech watches for this as he knows the volt readings must be around 13.8VDC to 14.6VDC or around that, more or less ballpark.


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## Hydros

NEXT, there is a test called the full field test. This is like the one where you turn everything on in the car and see if the alternator is putting out the needed amps and then some. (I think it needs to be performed at around 2,000 RPM). This pretty much has a known value. The field test pushes the alternator and regulator to it's limit and should be done as quickly as possible. This is good on an analog meter because you can watch the needle swing.

So there is a book/manual/guide that tells you what to look for.

Back to this part "_So the tech watches for this as he knows the volt readings must be around 13.8VDC to 14.6VDC or around that, more or less ballpark." _Most times a tech will increase the idle speed to get that alternator to charge the battery faster, so the testing is completed faster. That's OK. 

So we have an idea of the specs on the field tests, and we have an idea of the specs on the idle speed tests, or do we? This is where the fundamental flaw is. What is missing, and what are the average readings that the ignition system draws?


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## Hydros

We have an idea of the volts and amps on the full field test (or everything on test).
But it is in the idle speed test that fails to have the amp reading, as the tech is looking at only the volts. So what should be the amp reading? Well it happens to be the load or draw from the ignition system. That averages at around 10 amps with everything off. 
But sometimes or all the time the techs don’t care, or don’t know. Just park the car, the volts read good, that’s it, all done. 

Hmm…


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## Hydros

hmm slow night, better get these hints out and get off line. 
The battery tested good, the charging systems appears to be good and the tester itself is working correctly. 

But what about that amp reading. And what affects the amp readings. Could the amp reading be lower/higher? Remember the “everything on test”?


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## Hydros

Post anything, multiple guesses is OK. The first one with closest to the actually answer gets the $20.

OK here is the kicker:

The amp reading can’t get any lower, there is nothing left to turn off. So why would the amp reading be higher. Because something is on and causing a load, or something is just causing a load. 

When there is a load, the alternator keeps working, and working and getting hot over and over. Until it burns out. That load is from a battery with an internal resistance. But yet it tested good. Test it all day long, as many ways you like and with any equipment. It will test good. Now there was another machine made by Bear, part of the testing it did was to charge the battery. It caught bad batteries and borderline batteries. But I can’t recall or don’t believe it caught all borderline batteries with residence. 

An obvious way to test a much higher resistance battery or sulfated battery is by charging it and looking at the amp meter. It just never seems to get any lower than a certain value when charging at 2,10,40 amps, (can’t recall what amps the charger is set at, or at what the amps reading stay at). The battery gets hot, or the battery will just not take a charge. If this battery were used in an everyday vehicle, it would be too easy to spot. 

So, with everything off in the car, with the engine running and the charging systems stabilized, you should see around 10 amps a little more here and there is OK, but anything near double is too much. 

*So what would we see on the meter/s if a battery had an internal residence?*

Post anything, multiple guesses is OK. The first one with closest to the actually answer gets the $20.


I’ll check back Monday, good luck.


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## Hydros

OK Guys, biggest hint of them all, the answer has already been given, it's already on this page.

Tuesday I'll copy and paste the needed text to form the sentence.


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## Hydros

OK Guys I'm going to close this up around 9PM tonight so you have a few hours left for the $20., I'll post the answer on SD in a few days. But really, the answer is already on this page.


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## cashmoneyspeed

Bad battery being hidden by an alternator that tests good but is actually putting out too many amps. Alternator would test good at firstvsince the regulator is working. So with the car sitting for a period of time , the battery looses its charge but if you charge it and drive it, the charging system will seem like its all good. I would think there's an extra load from the ignition system. Maybe a shorted ignition switch?


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## Hydros

Hydros said:


> Post anything, multiple guesses is OK. The first one with closest to the actually answer gets the $20.
> 
> 
> 
> *So, with everything off in the car, with the engine running and the charging systems stabilized, you should see around 10 amps a little more here and there is OK, but anything near double is too much. *


after all these years, 
The correct answer is anything over the ignition draw is suspect. if you see anything near double the amps and the amps never fall, the only thing left is the resistance from the battery. These is no reason for such an amp draw when everything is turned off. There is also resistance from the wiring, but the question is regarding the bad battery, not what are the things that can cause the alternator to continually put out higher amps. 

This continue draw on the alternator can cause the alternator to fail.

for newer vehicles this may or may not be the same answer. 


*cashmoneyspeed*, good try, almost nailed it, but since you were the closest, you get the $20.00, PM me your paypal ID, or mailing address and to whom (or who) to make the check out.

Thanks to the other members that gave it a shot.


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## cashmoneyspeed

Thanks again, received payment just like he said :thumbsup::thumbsup:


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## cashmoneyspeed

Thanks again, received payment just like he said :thumbsup::thumbsup:


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