Is Conductance Testing Useful?

January 4, 2010  |   Posted in Blog   |   1 Comment   

Conductance testing is useful for determining the remaining life (or state of health, SOH) in a battery.  Many battery distributors and service centers use conductance testing on a regular basis for this very purpose and warranty processing.  However can conductance testing be used to establish a rating for a new battery?  According to Midtronics, a leader in conductance testing, no!    To quote their website,

“The Midtronics CCA value derived from conductance does not, however, determine the actual Cold Cranking Amps of the battery because that test includes a lengthy discharge of 30 seconds at a very high current rate.”

“The Midtronics CCA values are designed simply to mimic the initial starting characteristics of new batteries with a given CCA rating under the same operating conditions.
For example, if a battery that is rated at 600 CCA is measured at 500 CCA, it can be thought of as having similar starting characteristics of a new battery having a rating of 500 CCA if that battery is substituted with the test battery. It does not mean that the battery will pass a Cold Cranking Test at 500 CCA. It should also be remembered that the cranking power of all batteries increases with temperature and decreases with discharge and degradation.”

In talking with one of their engineers at the recent AAPEX show in Las Vegas and going through a demonstration of their product, it was clear that the Midtronics unit is not designed to set the CCA number, only to estimate it given a standard.  You enter the factory rated CCA data into the Midtronics machine and the machine returns a CCA that represents the battery’s state of health.

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Again to quote the Midtronics website:

“The most effective method for the establishment of a standard requires the performance of a timed discharge test to locate a cell or battery that performs to 100% of the rated discharge capacity. A conductance test can then be performed and a reference established. A sample of 30 or more new batteries can also be used to establish a standard. Without a set reference value, conductance testing can still be utilized to trend state of health, as batteries can be monitored through periodic conductance readings and the observation of deterioration over time.”

What is said above corresponds to what is said here by the BCI:

“Ohmic measurements are not a substitute for capacity testing and cannot be used to predict absolute capacity values.” For full text, see bci_ohmicreadings.pdf

For these reasons XS Power does not use conductance testing to rate our batteries.  Instead we use the BCI method of timed high rate discharge and have equipment in house to verify it.  In our opinion, this may explain why many have had disappointing results with Braille batteries as the ratings given from conductance testing on new lead acid batteries will be higher than an actual BCI test.  The real performance of Braille batteries should mirror their Deka equivalents (see www.eastpenn-deka.com .)

If Deka rates the battery at 200CCA one could count on it passing the BCI crank amp test at an independent lab.  Moving that rating to 360 CCA based on conductance test alone is misleading because the buying public assumes you are comparing apples to apples.  You are not.  Buyer beware!

Further the Midtronics machine returns only a CCA, CA (or MCA) estimated rating.  How does  Braille arrive at their Pulse Cranking Amps (PCA) 5 sec @ 80°F, Pulse Cranking Amps (PCA) 10 sec @ 80°F, Pulse Cranking Amps (PCA) 20 sec @ 80°F, and Pulse Cranking Amps (PCA) 30 sec @ 80°F?  The Midtronics machine they claim to use does not provide that information.  The basic lead acid chemistry will not allow for this type of performance from these sizes.  These numbers are not in harmony with the 200CCA/12Ah rating from the manufacturer.  One can only conclude that these numbers are calculated estimates, not measurements.

XS Power sells the highest performance AGM batteries on the market.  They are built with lead-tin technology which is the highest energy density among the AGM chemistries.   When it comes to buying a real racing battery, don’t fall for smoke, mirrors, and decals with inaccurate ratings.  Go with the same battery other winners are using right now, go with XS Power!