It should be noted that I own and spent my own hard earned money on all the impedance testers used in this article. I first noted these discrepancies years ago and tried to learn to translate the results from actual Ah capacity to what these devices spit out. I also spent aa great deal of time on the phone with the folks at Midtronics, & Argus while they were still in business, trying to come up with a translation "factor" from CCA to Ah capacity, for different battery types. Suffice it to say there is not one that is repeatable and reliable.


The Midtronics line of impedance testers are considered the gold standard for cranking capacity testing. Many battery manufacturers, such as Deka supply these testers. at great cost, to their resellers in an attempt to limit warranty replacements. This is great for trucking fleets and automotive applications but early on I was lead to believe these could be a good predictor of state of health / SOH for marine batteries too.. Boy was I mislead, at least in regards to Ah capacity, which is what really matters to boaters.. This particular tool is a 4 figure product... Don't get me wrong I love this tool and it serves many other purposes but predicting Ah capacity or SOH (state of health) as related to usable battery capacity, ummmm...well............????


So how did it do? As can be seen I accidentally programmed it for 810CCA when the battery is really rated at 800CCA. This really matters little because we are trying to figure out where the testers says this battery is in relation to the factory rating. If I had been printing a test receipt, for a customer, I would have changed it from 810 CCA to 800 CCA but not a big deal for this.


The Midtronics EXP-1000HD showed this battery performing at approx 109% of its factory rating or BETTER THAN NEW when USED. When the battery was brand spanking new it delivered 882CCA or 110% of the as new rating.


While this may be true for short duration cranking amps it is really an utter failure at predicting usable Ah capacity because we know for a fact this battery is down 30% of its as new factory 105Ah rating at just 73.4Ah's... Ouch......


RESULTS:


Factory CCA Rating = 800CCA

EXP-1000HD "New Battery" Results = 882CCA

EXP-1000HD "Used Battery" Results = 871CCA

Percentage of Factory CCA Rating "New Battery" = 110%

Percentage of Factory CCA Rating "Used Battery" = 109%

Factory Rated Ah Capacity = 105 Ah

New Tested Ah Capacity = 104.5 Ah

Used Ah Capacity When Compared to Midtronics = 73.40 Ah


For fairness this battery was still in my water-bath which is used to control battery temp to 77F during testing. The Midtronics measures battery temp as can be seen from the screen shot and the battery is at 77F just as it should be for a 20 hour capacity test..