BU-902a: How to Measure CCA (Cold Cranking Amp)

Discover why a good CCA reading does not always guarantee a good battery

Ever since Cadillac invented the starter motor in 1912, car mechanics explored ways to measure cold cranking amps. CCA measurements assure that the battery has sufficient power to crank the engine, especially when cold. A starter battery with low resistance promises reasonably good cranking ability, and a CCA reading of 400 to 500A is sufficient for most starter batteries. According to SAE J537, a CCA reading of 500A delivers 500A at -18C (0F) for 30 seconds without dropping below 7.2 volts.  [BU-904 How to Measure Capacity].


Courtesy of BMW

A diversity of battery testers have emerged that measure the internal resistance of a starter battery, the gatekeeper that correlates with CCA. These devices are the trusted carbon pile, the pulse-load tester, the non-invasive AC conductance method and the modern electrochemical impedance spectroscopy (EIS).

To test the CCA with a carbon pile, a fully charged starter battery is loaded with half the rated CCA for 15 seconds at a moderate temperature of 10º C (50º F) and higher. As example, a 500 CCA battery will discharge at 250A for 15s and the battery passes if the voltage stays above 9.6V. Colder temperatures will cause the voltage to drop further. The carbon pile simulates real-life load condition, detecting defects involving partially shorted cell (low specific gravity) that non-invasive methods might not catch.

Mechanics prefer small sizes and device manufactures have developed handheld testers that induce a momentary high-current pulse. Ohm’s law calculates the internal resistance on hand of the induced voltage drop and provides a CCA-equivalent reading. The test results of this device are similar to those of the carbon pile. The battery should be fully charged and the loads methods can estimate capacity.

The AC conductance method reads CCA by injecting a single frequency of 80–90 Hertz to the battery. These non-invasive units are small, stay cool during the test and the battery does not need to be fully charged. As with the other test methods, AC conductance cannot read capacity.

Critical progress has been made in electrochemical impedance spectroscopy (EIS). EIS has been in use for many years in laboratories to analyze diverse materials. EIS has been combined with complex modeling to estimate CCA. This also allows capacity estimations. The resulting multi-model electrochemical impedance spectroscopy is called Spectro for short. Spectro™ is a Cadex trademark. (See BU-904: How to Measure Capacity)

Accuracy has always been a question mark and CCA is especially difficult to verify. CCA is affected by state-of-charge (SoC) and and other factors. Figure 1 compares CCA readings taken with AC conductance and Spectro™ at different SoC. Both readings decline with lower SoC and AC conductance is affected more than Spectro™. Since batteries hover at about 70 percent when the car is brought in for service, the CCA readings between the two methods appear similar.

Figure 1: CCA accuracy on state-of-charge

The Spectro CA-12 provides stable CCA readings between a SoC of 100–40% (red); the values on AC Conductance drop rapidly with SoC (blue).

 


Figure 2 illustrates CCA readings as a function of SoC and battery performance. The CCA of Battery A with a capacity of 100 percent stays steady down to a SoC of 10 percent; Battery B with 37 percent capacity starts to show instabilities at a SoC of about 40 percent, and Battery C with only 22 percent capacity provides uncertain results. This test demonstrates that a health battery provides clear and measurable symptoms where the indicators of a weak battery are muddled.

State of Charge

Figure 2: CCA accuracy in relation to battery condition and SoC
The battery condition governs accuracy. Battery A (100%) is accurate to 10% SoC; Battery B (37%) to 40% SoC. Battery C (22%) delivers unstable results. Test condition: Batteries are discharged at 20A. CCA is measured every 10 min with Spectro™


No single instrument can evaluate all battery anomalies and rapid testing only provides rough estimation. A micro-short in a cell, for example, can only be identified by applying a load after a rest period or checking the specific gravity of the electrolyte. Rapid-testing might pass the battery as good because a charge covers up the anomaly.

All test methods provide outliers and no clear accuracy specifications can be given. Certain defects are easier to detect than others, and as there is a high probability that it will not rain in the Mohave Desert today, forecasting rain in London is more complex. There are no ideal battery test methods and scientists see future in electrochemical impedance spectroscopy.

Last updated 2015-05-26


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Comments

On August 31, 2011 at 1:06am
sumesh arora wrote:

what is the cost of spectro CA-12 battery tester?

On September 7, 2011 at 11:21pm
Ray Grant wrote:

what is the cost of spectro CA-12 battery tester? I am possibly interested in the purchase of lead acid battery capacity meter

On November 5, 2011 at 9:37am
Troy Mikkelson wrote:

Cost of the CA-12 is in the 4 digits before the decimal point region.  It isn’t intended for hobbyists, but shops that service/sell batteries.

The flipside is that Cadex IS the #1 Battery Test/Charge platform for all chemistries for over 20 years, so there is no doubt that the CA-12 is a quality product.

On February 1, 2013 at 7:29am
Alex wrote:

A better method of explaining what capacity is, is to have a swimming pool and a kitchen sink filled with 12 inches of water each…lets assume an inch of water equates to 1 volt…after all, voltage is a pressure and with 12 inches of weater in a vessel, a certain fixed pressure is realized at the bottom of it.

You now have a 1” diameter hole at the bottom of the swimming pool and the kitchen sink.

It is easy to see how the voltage would drop after a minute of flow as the level in each vessel decreases.. The level in the swimming pool will hardly change, whereas the level in the kitch sink will be near empty.

On February 3, 2013 at 9:55am
Chris Barry wrote:

Could someone please provide a better definition of CCA? In particular, what will the load be during the course of the test? There would seem to be three options, constant load resistance, constant current and constant potential. Using either of the first two would seem to make it effectively unmeasurable, at least with any degree of precision, as it would be necessary to predict the the performance of the battery before starting the test.

A test at constant voltage, on the other hand, should be quite easy to perform. Even with quite simple equipment - a rheostat moved by a motor, controlled by a circuit which monitors the battery voltage. With modern power semiconductors it should be possible to do the same job more quickly and with no moving parts. The significant result would then be the current flowing at the end of the test.

On February 4, 2013 at 3:43am
Rajendra wrote:

Am need purchased the 12 Volt x 2 batteries , But i want a imfirmation of cranking in nos.?
Rgds,Rajendra

On February 4, 2013 at 3:45am
Rajendra wrote:

Am need purchased the 12 Volt x 2 batteries 32 AH & 74 Ah, But i want a imfirmation of cranking in nos.?
Rgds,Rajendra

On June 8, 2013 at 11:54pm
Chad wrote:

What is the difference in construction between a 650 CCA battery and a 950 CCA battery?

On July 16, 2013 at 11:09pm
jonadab wrote:

what is cca reading for 12v battery?

On July 18, 2013 at 12:54pm
reason wrote:

The reason is 12V battery CCA is =  CCA of 12V battery,
so, when 12V battery=24Vbattery/2, then 12v battery*2=24V battery,
so CCA is CCA

On July 18, 2013 at 12:55pm
New Reason wrote:

THEE CCAAA OF 12V BATTERY IS AROUND 500A

On January 7, 2014 at 3:17pm
Alvan W. Atkinson wrote:

Since batteries tend to fail in cold weather probably because less capacitance available as the available capacitance falls linearly with temp (flooded lead-acid)  Why not put a battery in a progressively cold environment—programmable refrigerator and graph resistive discharge(15sec)  carbon load or other at decreasing temps.  Or test at 0C vs 50C.
Would seem this relatively simple stress test, although it would take time to change temp of battery would increase reliabilty of prediction of reserve CCA. ????

On February 26, 2014 at 5:32pm
Aleksander Vyurkov wrote:

I am looking for modern testers (non-invasive) for testing NiCd flooded starting batteries. Manufacture - SAFT, Battrey type- SPH 250 &300;. Please advise which testers are available for NiCd starting batteries.

On April 19, 2014 at 6:22pm
Shannon wrote:

I have a bunch of 12v car batteries that are unlabelled (about 50) so I have no idea of the manufacturer OR the cca.

What device can I connect to the batteries to find out what the capacity of them is now without entering the original cca (as I have no idea what it would be)?

On June 13, 2014 at 6:35am
Bob Nuckolls wrote:

Capacity and CCA are not tightly related. A rather small battery (low capacity) can demonstrate exemplary CCA ratings while some really big honkers will turn in disappointing CCA numbers. I have a 75 pound, group 31 battery on my bench right now with a demonstrable capacity of over 120 ampere-hours . . . but it drops to 9V at 600A load. Conversely, I have some 18 pound batteries in the 18Ah class that will dump 500+ amps at 9V.

Clearly, the internal impedance of the batteries with a smaller CAPACITY is superior to the larger battery with 5x the capacity.

A detailed study of the condition of your batteries can be conducted by first topping them off with a quality charger-maintainer. Then load-test to 9V with a carbon pile LOAD tester.  Top off again and the CAPACITY test with something like the West Mountain Radio CBA capacity meter (runs battery down and counts electrons)..

A comparison of the LOAD and CAPACITY numbers for the family of test article will gie you the best measure of their condition and potential performance.

On July 29, 2014 at 10:53pm
Rudraiah Naidu wrote:

how we would conclude the battery plate conversion quality during the process of curing followed by drying.,

On November 15, 2014 at 12:43am
barry wrote:

If a battery is 650A, does that mean it is 650 AH? where as 120AH battery is quite big in size ( trucks have it under hood) . I dont’ understand how come a small battery ( car battery )have a 600A label on it while it looks like 40AH car battery. Kindly provide a bit of example.

In india, we have car batteries ranging 30Ah-45Ah . Truck batteries ranging between 100Ah to 140Ah.
But as to why in USA and Canada, Cars batteries of same size have label of 600A on it?????

And bigger batteries for trucks have 1000A label on em’.
Any point clearing my confusion would highly be appreciated.

On December 19, 2014 at 11:00am
David wrote:

I think you mean full-fledged, not full-fletched. While this article appears to be informative, such incorrect language use degrades professionalism, and this site is named battery university.

On March 7, 2015 at 4:47pm
Wole Adu wrote:

@Barry, the 600A refers to the CCA (Cold Cranking Ampere) and not the Ah.

On April 9, 2015 at 12:16pm
Lisa wrote:

i was told I needed a new battery. They said the cold cranking amps rated 600 measures 279 c.c at my last check up at the car dealer. Is this true? Do I really need a new battery?

On May 28, 2015 at 2:33pm
Wole Adu wrote:

@Lisa 279CCA will not start up your car, what you can do is ti regenerate your battery outside that buy a new one.

On July 13, 2015 at 1:28pm
Jessica wrote:

Hi, I just had my car battery tested and they said my battery was low and needed to be replaced.  I’m confused though because they guy said it read 325 out of 500, and I am not sure what these numbers are referring to?  Everything I have found regarding car batteries are discussing voltage (should be at 12.6 for a good battery?)  So confused. Thanks for your help.

On July 18, 2015 at 1:53pm
wole adu wrote:

325 you were told is the CCA (Cold Cranking Ampere), which means a battery’s ability to start an engine in cold temperatures.

On July 18, 2015 at 1:56pm
wole adu wrote:

CCA (Cold Cranking Ampere), is the rating used to define a battery’s ability to start an engine in cold temperatures.

On August 17, 2015 at 7:36am
Mike_Massen wrote:

Have a pair of 24AHr SLA Lear jet APU starter batteries (in parallel) for a Holden Apollo 2.2L 4cyl (Rebadged Toyota Camry Wagon), these are the high quality so called ‘pure lead’ Hawker (narrow red) batteries same as certified for avionics, they were initially used in a high end UPS at the local Curtin University library server room & reached their end of life in ~2006.

They’ve been used in my car since & still start fine, though they’re a bit down on CCA from new ~600A ea, last time I checked their parallel CCA was ~950

In summer, when daytime temps exceed 35 C & up to 44 C, they sit in water in the engine bay in a plastic battery box - sometimes in town I’ll to drop into a local coffee shop & get a couple of take-away cups of ice & flood that into the battery box. Minor corrosion on the stainless steel terminals isnt a problem as its easy to brush off. In winter when it gets down to approx 20C the box is dry & they’re fine.

Batteries both date coded 1996


Read more at: http://phys.org/news/2015-08-ohm-drop-in-car-battery.html#jCp