PUBLIC APOLOGY: First let me begin this by eating some public CROW. Over the years I have recommended these testers for boat owners or techs to use, as had the ABYC and other reputable organizations. While I have always maintained a get a baseline > moving forward manner for use, it seems even this may not be as accurate as I had initially thought it was. While this type of use, baseline > forward, may give an indication of changes in the battery they do not easily correlate as well as I initially thought, or was lead to believe by the manufacturers of these products.
It was not until I got heavily involved in actual physical capacity testing (20 hour capacity tests) that I realized the extent of the errors in these devices as related to usable Ah CAPACITY. The manufacturers make them sound like the second coming of God, and they may be for cranking amps, but they perform rather miserably for translating to the kind of data we as boaters need for our low rate discharge house battery banks.
I am not the kind of guy who likes or wants to mislead folks, quite the opposite, so I have to be honest in this article and eat some crow.. I am also not the kind of guy who, just because he owns something, it has to be the best. This is just not at all my style and when I suggest things and then find out that they may be giving erroneous information I just need to tell it like it is and correct my initial assertions.. I will always be honest when things don't work, as I had hoped, and this is one of those cases.
Impedance Testers Vs. Ah Capacity Testing:
Over the past 5 months I had to opportunity to run hundreds and hundreds of hours of battery testing for one of the sailing publications. I can't discuss the testing outcomes for that article but that testing spun off some other interesting tid-bits. What I can show you is how actual 20 hour Ah capacity tests compare to impedance battery testers. The results are more shocking than you'd probably ever imagine..
For this testing all the batteries were cycled up to rated capacity and a baseline Ah capacity was established using the average of two controlled 20 hour capacity tests to BCI testing standards. This particular battery tested new, once "cycled up" to capacity, at 104.5 Ah's.
After the rather brutal testing was completed the now diminished tested Ah capacity of this battery was approx 73 Ah's or a loss of 30% of its usable Ah capacity. So how did the impedance testers compare to an actual 20 hour capacity test? You're about to find out.....
CLICK ANY IMAGE TO MAKE IT LARGER