Just for grins I was in Harbor Freight one day and I grabbed the Centech impedance tester. It was under $100.00 but is, shall we say, sloppy when compared to the Midtronics or Argus.


In this shot the Centech/HF tester is making this very tired battery appear to be a rock star. A battery that is down 30% of its factory rated Ah capacity is anything but a "rock star". If buyers of this tester believe it to be true their actual capacity could be WAY off.


RESULTS:


Factory CCA Rating = 800 CCA

Centech Results = 1018 CCA

Percentage of Factory CCA Rating = 127%

Factory Rated Ah Capacity = 105 Ah

New Tested Ah Capacity = 104.5 Ah

Actual Ah Capacity When Compared to Centech = 73.40 Ah


Results for comparing Ah capacity to CCA = FAIL!!!!!!!!!!!!!!!!



I honestly used to believe I could learn to translate the impedance data to Ah capacity but every time I though I had it nailed, a curve ball was thrown at me.


If you want to know cranking ability of a battery these testers can be very useful.


If you want to know your batteries SOH as related to Ah capacity fogedaboutit.


So how can you use one? I still suspect we can draw "some" conclusions from an initial baseline to a future test using the same tester and the same batteries. I have developed lots of these sorts of data-sets for my Argus and Midtronics but they keep proving me wrong.


The bottom line is that impedance testers simply do not translate well to Ah capacity, and on low rate discharge house banks, Ah capacity or usable capacity is ALL THAT MATTERS.. I wish they were more accurate because it would make my life MUCH easier, but I am sorry to report, they are not.


I have no qualms with the Midtronics for predicting cranking capacity, and suspect it is rather accurate. The Harbor Freight / Centech on the other hand I would urge using caution in taking it at face value for cranking ability....