Relationship Between Battery Cold Cranking Amps and Capacity

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The difference between successful people and very successful people is that very successful people say 'no' to almost everything.

— Warren Buffet. Many people do not accomplish their goals because they spend the bulk of their time on items that really are just distractions. You need to look at your time usage, figure out which recurring items are taking time, yet providing little real value, and minimize them.


Introduction

Figure 1: Typical Flooded Cell Car Battery.

Figure 1: Typical Flooded Cell Car Battery. (Source)

Many battery manufacturers do not specify the Ampere-Hour (AH) ratings for their automotive products because Cold Cranking Amperes (CCA) are more important in automotive applications than AH ratings. Car applications tend to focus on the ability of the battery to crank the engine when both the battery and car are cold. While reading a post on an automotive forum about batteries, I saw the following statement made about the relationship between a battery's CCA and AH ratings.

I have read on the box of that Inox battery conditioner that for a battery over 600 CCA you simply multiply the CCA by .07 to give you the Amp Hours for that battery …

I have seen this statement before and did not believe it because batteries intended for capacity-dependent applications (e.g. backup power) are designed differently than batteries intended to deliver surge current (e.g. car batteries). I decided that it was time that I demonstrate that this relationship does not hold for specific batteries, but does have some merit for batteries in general.

Because France requires battery manufacturers post the AH specifications for all car batteries, I was able to find both CCA and AH specifications for a number of car batteries on European web sites. Once I gathered the data, I generated a graph that shows that there is not a general relationship between the CCA and AH. All you can say is that on average, increasing CCA ratings means increasing AH ratings. There is no simple relationship between AH and CCA that holds for all lead-acid automotive batteries.

All the analysis was done in Rstudio.

Background

Methodology

My approach was simple:

  • I randomly chose four car batteries from five different vendors.
  • I generated plots of AH versus CCA for each manufacturer.
  • I also generate a plot of AH versus CCA for all the batteries.

Data Set

Figure 2 show the set of battery data that I gathered. The batteries were randomly chosen from among the hundreds of choices.

Figure 2: List of Random Chosen Car Batteries.

Figure 2: List of Random Chosen Car Batteries.

Analysis

Figure 3 shows my graph of AH versus CCA for data of Figure 2. I also fitted lines to each of the vendors data. Note that there is a wide variation in how AH varies with CCA for each vendor. There is no formula that provides a good fit between AH and CCA for all automotive batteries. The fit is not even good for batteries from the same manufacturer. For a similar chart of batteries from a single manufacturer, see Appendix A.

Figure 3: Plot of Five Manufacturers, Four Batteries Each.

Figure 3: Plot of Five Manufacturers, Four Batteries Each. Note that I "jittered" the data so that points from different vendors would not sit on top of each other.

Figure 4 shows my overall curve fit. This line has a slope of 0.0688 AH/CCA, which agrees with the 0.07 AH/CCA statement on the Inox conditioner box. However, you can see that specific batteries are scattered far from the line.

Figure 4: Linear Curve Fit for All the Data.

Figure 4: Linear Curve Fit for All the Data.

For those who like to look at curve fit statistics, I also include Figure 5. The statistics shown are for lines that are function of CCA alone (Figure 4), and CCA and Brand (Figure 3).

For AH versus CCA line, we see that CCA is a very significant factor (red underline) but our R-squared value (fraction of variability explained) is only 50%. For the AH versus CCA and Brand line, we see that CCA is very significant and some Brands are significant,  but our R-squared value (fraction of variability explained) is only 85%.

Figure 5: Curve Fit Statistics.

Figure 5: Curve Fit Statistics.

Conclusion

While it might be tempting to estimate the AH rating of a battery from its CCA rating, there is not a simple relationship between these two battery parameters.

Appendix A: Yuasa Example

In Figure 6, Yuasa has published a graph similar to my Figure 3. Notice how the lines have roughly the same slopes, but different intercepts. As I always say, a battery is a nonlinear function of everything.

Figure 6: Battery CCA Versus Capacity. (Source)

Figure 6: Battery CCA Versus AH. (Source)

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15 Responses to Relationship Between Battery Cold Cranking Amps and Capacity

  1. pracha says:

    Great info, thanks!

    so what would be a good estimate of the CCA for a Maintenance Free 12Volt battery of Actual 68AH rating ?

     
    • mathscinotes says:

      This post discussed the accuracy of the "rule of thumb" AH = CCA*0.07. I showed that the relationship roughly true for all lead acid batteries above 600 CCA, but there are significant errors with respect to individual batteries. Using this relationship, a 68 AH battery would have 970 CCA. However, the true value varies widely depending on the battery construction. If you look at Figure 2, there are two batteries that are close in capacity to yours. The 69 AH battery from Northstar has 930 CCA, and the 70 AH battery from Yuasa has 760 CCA. You can see that the results for an individual battery can vary widely.

      mark

       
  2. Ramutsikabotlalo says:

    Reading your article and the comment you responded to, I'm in South Africa and my car uses a battery labelled, EXIDE 631 -38Ah. It has no other label's or stickers that represent any CCA rating, I'm wondering what 631 represents but on looking up Exide 631, 631 seems to represent the type of battery it is. Now, I'm confused! If Exide 631 represent's the type of battery, then what does that number actually represent about it really and with it can I determine the CCA rating of my battery?

     
  3. mohammed saif says:

    Hello
    The battery analyzer is depending on CCA capacity, but all solar batteries capacity are AH, so I want CCA vs AH capacity, please.
    Thankfully

     
  4. Pingback: Battery - Chevy Traverse Forum: Chevrolet Traverse Forum

  5. Peter Evans says:

    Hi,
    Could you please help. Battery manufacturers, retailers and even dealerships have either refused to answer, or are seemingly clueless.
    It all started when a scan of my X350 series Jag threw out a code which says 'battery is voltage is out of range'.
    After much discussion on Jag forums it seems the spec for the car is a 90ah silver calcium battery.
    It appears no one in US manufactures such a battery. What am I missing here?

     
    • neal says:

      If your battery is out of expected/normal voltage range, then it almost certainly has a low charge. Lead acid batteries appear to have charging voltage about 14.5v , standby voltage about 13.5v, and nominal voltage of 12v. The chemistry of the lead plates and acid matrix produces only one voltage range from zero with no charge to about 13.5 fully charged, while the amperage varies with the size of the battery: greater or fewer lead plates and acid matrix.

       
    • mathscinotes says:

      In general, I agree with Neal. I would mention that I do occasionally encounter shorted cells.

      mark

       
  6. Stas says:

    Good study! but you could make a couple of practical conclusions. For example if you'd give linear equation for bottom and top lines from figure 3, one could use them to calculate lower and upper bounds. Say I'm interested in lower/upper bounds formulas for calculating capacity using CCA, in my country only CCA is written on batteries.

     
  7. Myo Ko Ko says:

    Hello;
    I would like to know the battery cell damage and CCA range.
    Thank you

     
  8. neal says:

    Another way to look at this is to consider a 14Ah battery example. It can provide 1.4A for 10 hours or 14A for 1 hour. At 1 hour, it delivers 14A for each o f 60 minutes, so 840A are available in one minute. When delivering surge current, CCA, about 20 seconds is the maximum duration necessary, and 280A would be available. Comparing this to the rule of thumb is within reasonable approximation?

     
  9. OptimasSuck says:

    NICE Chart... It's proof positive in addition to our successful long term trial tests
    In our Vintage British 60's Sports car club.. Where sealed batteries are a MUST to avoid acid damage... we've discovered that since our cars only require 300-400 CCA's... we experimented with scooter / wheelchair / Lawn Tractor / Motorcycle SLA AGM batteries.. with Great Success... Not only are they a LOT smaller, and LIGHTER.. with cheap onboard pulse desulfators, we can make a $30 5lb battery with a 6 month warranty last 5+ years.... Many of us are still going strong after 7 years... and mount 2 in parallel in a battery box... you even double the AH's that way....... Terminal type makes NO DIFFERENCE... you can buy / make adaptors for ALL of them..... and those CHEAP $13 1.5w car solar maintainers at Harbor Freight... work AWESOME too...... Now that we've successfully proved it works long term.. we're spreading the word to all our friends... Practically EVERY 4 cyl and 6 cyl car can use this system and save a TON of money.. LONGER Lasting $30 single battery / $40 2 battery setups compared to the waaay overpriced rip-off $250 + Optima / Odyssey / Exide / Corporate Greed car battery industry....

     
  10. Savita says:

    I want to know

    How can we increase battery CCA keeping Ah same.
    For e.g 75Ah battery having CCA 650 and 65Ah battery having CCA 600.How can we increase CCA of 65Ah battery to 650 keeping same Ah.
    Or how can we increase CCA of 55Ah battery to 650

     
  11. I am trying to find out the CCA for Powersonic PG12V120FR : 12V 120AH. Can some one help me.

     
  12. stewart says:

    hi cam u help i have a 700A battery i have a Battery Analyzer Diagnostic Tool which wants me to measure cca is there way to convert or just put 700 in to it for cca

     

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