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#4617597 - 12/29/17 09:46 AM battery tester - internal resistance
Donald Offline


Registered: 03/21/04
Posts: 20450
Loc: Upstate NY
Got a new conductive battery tester that provides internal battery resistance in addition to the CCA.

So what is a good resistance and what is no good? Can it tell a bad cell? Sulfation?
_________________________
2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)


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#4617601 - 12/29/17 09:50 AM Re: battery tester - internal resistance [Re: Donald]
Rand Offline


Registered: 08/20/03
Posts: 12638
Loc: NE,Ohio
Going from memory

anything over 10 is terrible.

normal is around 4?

They are a good tool to have but not a conclusive way to test a battery.

I usually like to use a load tester as well when possible.. charging the battery first if needed.

But for basic stats they usually work pretty good.


I recently tested a 2 year old AAP silver 650CCA battery in a 2003 taurus.

It was showing low charge, 12.1v 8.3 resistance, 375CCA

I fully charged the battery overnight. The charger gave me an error which I think means the resting voltage is dropping too fast.(it kept float charging the battery as needed)

Capacitive tester now says its good for 480CCA.

Something is going on with the battery.. probably replacement soon.

If the battery is at 12.1V next time I go over I'll tear it out and replace it.

Luckily its garaged so its not started outside at 0f and below etc.. so even weakened its ok for now.
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#4617605 - 12/29/17 09:52 AM Re: battery tester - internal resistance [Re: Donald]
motor_oil_madman Offline


Registered: 11/29/09
Posts: 4845
Loc: Houston, Texas
Go buy a duralast gold battery from autozone. I haven't paid for a battery in like 8 years. lol They only last like 2 years. I thought my truck was just hard on batteries, nope my brother put one in and it was flat dead after 2 years. Couldn't even unlock the door. They have a 3 year free replacement if I remember right.


Edited by motor_oil_madman (12/29/17 09:53 AM)
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#4617622 - 12/29/17 09:58 AM Re: battery tester - internal resistance [Re: Rand]
Donald Offline


Registered: 03/21/04
Posts: 20450
Loc: Upstate NY
Originally Posted By: Rand
Going from memory

anything over 10 is terrible.

normal is around 4?

They are a good tool to have but not a conclusive way to test a battery.

I usually like to use a load tester as well when possible.. charging the battery first if needed.

But for basic stats they usually work pretty good.


I recently tested a 2 year old AAP silver 650CCA battery in a 2003 taurus.

It was showing low charge, 12.1v 8.3 resistance, 375CCA

I fully charged the battery overnight. The charger gave me an error which I think means the resting voltage is dropping too fast.(it kept float charging the battery as needed)

Capacitive tester now says its good for 480CCA.

Something is going on with the battery.. probably replacement soon.

If the battery is at 12.1V next time I go over I'll tear it out and replace it.

Luckily its garaged so its not started outside at 0f and below etc.. so even weakened its ok for now.


I have a carbon pile load tester also.
_________________________
2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)


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#4617674 - 12/29/17 10:37 AM Re: battery tester - internal resistance [Re: Donald]
CT8 Offline


Registered: 10/09/14
Posts: 10946
Loc: Idaho
you want a load tester.
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#4617694 - 12/29/17 10:53 AM Re: battery tester - internal resistance [Re: CT8]
Donald Offline


Registered: 03/21/04
Posts: 20450
Loc: Upstate NY
Originally Posted By: CT8
you want a load tester.


I have a carbon pile load tester. The new tester is just one more tool to better diagnose things.
_________________________
2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)


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#4617755 - 12/29/17 12:03 PM Re: battery tester - internal resistance [Re: Donald]
JHZR2 Offline



Registered: 12/14/02
Posts: 41773
Loc: New Jersey
Originally Posted By: Donald
Got a new conductive battery tester that provides internal battery resistance in addition to the CCA.

So what is a good resistance and what is no good? Can it tell a bad cell? Sulfation?


ESR (internal resistance) is battery design and size dependent. There's no good or set value that you can compare across all batteries.

It's also temperature dependent.

And state of charge dependent.

Some vendors offer new battery impedance. Sometimes you can find comparative values from high rate ups batteries, which are similar in design to an SLI battery (because they're designed to give max power for a few seconds to a few minutes).

Changes over time is how you should be looking at it.

Its really no different than doing a load test.

Vt=Voc-IR

Load testing with a known current yields the "R" value by calculating voltage drop. These other testers just infer it another way.

Another way to look at it, based upon the fact that you know a battery's voltage absolutely, is how much resistance would keep you above, say, 10.7V when cranking at 150A.

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#4617804 - 12/29/17 01:11 PM Re: battery tester - internal resistance [Re: Donald]
Linctex Offline


Registered: 12/31/16
Posts: 6148
Loc: Waco, TX
Buy a battery desulphator, and also make sure to "equalize" the cells (this takes a special 16v-18v charger)

That'll add another couple years of life to it.
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(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."

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#4618007 - 12/29/17 05:24 PM Re: battery tester - internal resistance [Re: Linctex]
Kira Offline


Registered: 08/19/10
Posts: 5214
Loc: Champlain/Hudson Valley
This won't help...but.

Years ago I took a fairly detailed electric class which was offered at work.

All I can recall is that a battery's internal resistance was needed for many of our calculations.

Many of us had never heard of IR before. The guys in the class who didn't "get it" COULD NOT reconcile the existence of resistance in 40 pounds of material.
"Batteries make electricity" they'd squawk.

When a battery begins to weaken within a proper time frame we don't spend too much time doing all the math. The poor thing is shown the door and may go through a battery revival protocol. I wonder what the success rate is.

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#4618426 - 12/30/17 02:18 AM Re: battery tester - internal resistance [Re: Kira]
WhyMe Offline


Registered: 12/18/12
Posts: 512
Loc: Washington for now
they are so cheap now( $30 ) that i bought one just to play with . like any new toy/tool i check all the car batteries i could find. one year old batteries were mostly 100% . 3 year old one about 65-75% internal resistance was 4-5

i tried it on a old spiral battery i have been trying to bring back to life. voltage was 12.3-4 . resistance was 375 and it showed 7 cca. i don't think this batt is going to come back to life . LOL Time to scrap it.

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#4619172 - 12/30/17 08:18 PM Re: battery tester - internal resistance [Re: Donald]
spackard Offline


Registered: 03/24/11
Posts: 1714
Loc: CA
One thing I've tried is capturing the min voltage during a start, with a DMM that has a setting to capture min voltage. Below is from an 18 month old Deka X2 Group 35 battery, living in So Cal.

Charged up battery, let sit overnight, then put my Agilent DMM onto it and captured the min voltage at the terminals when starting.
Ambient temp: 60F (overnight: 55F).
12.673V before test (driver door open); 10.581 min voltage captured.

Documenting a good test, then, over time, what it'll look like when questionable.
This type of test isn't one a parts counter person can do, but is a nice data point to have on a personally-owned car. To me, when the starter motor was stationary, drawing the most amps, the min voltage still was decent. A "bad battery" to me is usually one insufficient to start the car.

As far as impedance, I've seen 4.666milliohms on a new battery, 5.77milliohms on an 70% life left one.
There was one bad battery I had that measured:
11.63V, 77.35milliohms, 70°F, 1 hour after p.m. drive home.
Yet, it would quickly taper off when put on a charger.
Then it measured:
12.78V, 10.45milliohms, 269.1 measured CCA, < 40% capacity left.

I think the higher the impedance the lower the starting current (least it works that way in supercapacitors), so you want a low number. But, as I said in another thread, I don't have
much confidence in these things being able to call a battery good or bad.
Decades of experience, and a few dead chickens, are helpful.
I think if I had a submarine full of batteries I'd be doing monthly tests and graphing, looking for trends.

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#4619197 - 12/30/17 08:43 PM Re: battery tester - internal resistance [Re: Donald]
JHZR2 Offline



Registered: 12/14/02
Posts: 41773
Loc: New Jersey
Yes lower impedance the more current it can source. But it is also a matter of time/energy. That's always one of the issues, is that it can show a good voltage but have no real capacity behind it, and then polarize real quick and be flat. Then it will charge again nicely and be flat.

Add in shredded plate sludge and you can also have a high impedance short in there, which slowly bleeds energy.

I like to watch cranking voltage minimums too. It's the ultimate load test. However, you do need to know how many amps are being pulled by the starter. Contrary to popular belief, it's most likely not 300-500A. But you do want to know what it is, and then all that is also temperature dependent.

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#4620582 - 01/01/18 12:27 PM Re: battery tester - internal resistance [Re: JHZR2]
George7941 Offline


Registered: 05/10/05
Posts: 2158
Loc: Toronto, Canada
Yes, it is most likely 300 - 500 amps. My 4.3l motor has an inrush current of about 600 amps when the amp draw is monitored on an oscilloscope. So 300 - 500 amps is about right for somewhat smaller motors.
_________________________
2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.

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#4620629 - 01/01/18 01:11 PM Re: battery tester - internal resistance [Re: Donald]
JHZR2 Offline



Registered: 12/14/02
Posts: 41773
Loc: New Jersey
Inrush is not cranking. I suspect your 4.3 has a 1.2-1.5kW starter, which is 120-150A sustained cranking.

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#4620929 - 01/01/18 05:44 PM Re: battery tester - internal resistance [Re: JHZR2]
George7941 Offline


Registered: 05/10/05
Posts: 2158
Loc: Toronto, Canada
You are spot on with the figures for my starter, it is 1.2 kW and draws 120A hot and about 150A when engine is cold.

Agreed, inrush is not cranking. If you wanted to evaluate the internal resistance of the battery, it is best to measure battery voltage when current is at maximum, i.e. inrush. Of course you do need a scope to do this.

I now understand that when you mentioned cranking voltage minimums, you meant what the battery voltage drops to under sustained cranking
_________________________
2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.

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