Thank you for the posts and so sorry for the late feedback as trying to catch up with the relevant people is difficult whilst travelling.
I think its best here to start at the beginning with regards to battery testing.
One thing we all agree on is that testing batteries conclusively is near impossible without following the specific criteria laid down by the various industry standards. To follow such criteria will often leave the battery unserviceable!
We must not confuse the industry standard method of battery testing (SAE EN DIN) with the Pico Diagnostic (PD) battery test even though the results stated are in the same units of CCA
The CCA rating of any battery is a complex figure arrived at by design, therefore, any battery test result (Measured CCA / Percentage of Specified CCA) obtained during a PD battery test can only ever be an instantaneous, calculated estimate based on the measured resistance of the battery.
With the Pico Diagnostic battery test with have the advantage of safely drawing current from the battery where others don’t. (The cranking performance test)
Drawing current during the cranking phase allows for an “instantaneous CCA estimate” in the field. This could never match the conditions specified by the industry standards with regards to time, load and volt drop given we are cranking for minimal time (Approx. 1 second) with no control over the load from various open circuit voltages (OCV’s) to varying volt drop levels.
The fundamental value assisting with the estimation of instantaneous CCA is battery resistance and is calculated in the example below:
OCV =12.20 V, Lowest recorded Voltage = 7.23 V, Voltage drop = 12.20 – 7.23 = 4.97 Volt Drop
Battery resistance is calculated from peak starter inrush current using Ohms law:
Maximum inrush current = 560 A. Battery resistance 4.97/560 = 0.008875 Ohms
Estimated instantaneous CCA is then calculated for each industry standard based on instantaneous measurements taking into consideration battery recovery rate post cranking.
The battery test results then display the instantaneous Battery Capacity CCA value (447 CCA EN) using the figures derived from the calculations above where the specified battery CCA value was 468 EN. (Entered by user) 447 CCA is therefore 95% of the specified 468 CCA EN.
Displayed as Capacity is 95% of 468 EN.
Moving onto some additional questions.
What is the meaning of the Charging Circuit Status, E.g. Charging at 110 % ?
Charging at 110% is based upon battery voltage deviation from a known constant.
The “constant” used is the nominal voltage of a 100% charged Lead Acid battery being 14.4 V with an OCV of 12.6 V
The nominal voltage of a 100% charged Lead Acid battery is then compared to the charging voltage recorded during the charging of the battery.
E.g. Battery charging at 14.6 V
Nominal voltage (100% SOC) = 12.6 V
Nominal total deviation = 100% charged (14.4 V) – 100% SOC (12.6 V) = 1.8 V deviation
Battery voltage deviation for (battery charging at 14.6 V) 14.6 V - 12.6 V = 2.0 V
Nominal battery voltage deviation (ratio) 2.0 V / 1.8 V = 1.11
Charging status % is therefore Nominal voltage deviation (ratio) x 100 = 111%"
CCA calculation does not appear to change when selecting SAE, EN or DIN, Why?
Having spoken to the software engineers, this is possible post capture but perhaps not very intuitive.
With your test results on screen, (saved using the SAE standard for example) Select EN and then click analyse. The Instantaneous estimated CCA results will then change to suit the relevant standard selected. The same can be said for changing from Lead Acid to AGM batteries. Altering the temperature value post capture will change the results in real-time without having to select analyse
Do we consider stating CCA% with Capacity misleading and not possible based on our test procedure?
The results obtained are an instantaneous estimate of the relevant industry standard selected by the user, and like any battery tester, will provide and “estimate” only. The results obtained are most certainly accurate based on the formula mentioned above.
Different battery failure types will impact the results differently so resulting in some faulty batteries passing the relatively short PD test?
I cannot disagree with this statement but the same can be said for the “Impedance” type measurement/testers too. There is no fool proof method for testing 100% of all battery faults but we can be on our guard when testing batteries for all vehicles.
Perhaps the fundamental check for technicians when testing battery’s is to not rely solely upon the CCA rating stated on the battery. Whilst this is generally correct for the battery it is not necessarily correct for the vehicle. This could most certainly manifest itself as a “Battery Pass” based on an example CCA rating of 350 when fitted to a vehicle requiring a CCA rating of 850.
During cranking, the delivered current will most certainly result in an instantaneous estimated CCA rating of “Capacity is 100% of 350 SAE”, the giveaway however will be the recorded “Lowest Voltage”
Given we are testing for an Instantaneous Estimated CCA value in these scenarios we should repeat the battery test perhaps twice more whilst monitoring the Lowest Voltage and final capacity rating as we are likely to see a pattern such as Test 1. 100% of 350 SAE, Test 2 85% of 350 SAE, followed by Test 3 indicating a rapid decline, e.g. 30% of 350 SAE accompanied with a hideous Lowest Voltage value. In such a scenario battery capacity is clearly insufficient (Too low)
Remember a battery of this failure type is obviously not sufficient for this vehicle requiring a CCA rating of 850 but may prove serviceable for vehicles requiring ratings of 350 CCA and below.
Testing on anything less than a fully charged battery produces non-linear loading and so inconsistent battery test results?
Once again you cannot disagree with this statement/question. For the PD battery test to function, the vehicle must a least crank / start and therefore the battery is required to be in a reasonable state of charge. The industry standard tests require conditioning of the battery to impossible levels that no battery test can claim to simulate. (There are pro and cons of all tests)
Often one of the test results from a variety of battery testers will be “Battery requires recharge” in which case inconclusive results may have been obtained. (Alarm bells have to be ringing with such test results if OCV value is normal)
With regards to non-linear loading, the algorithm Pico use to calculate the final result factors in a number of variables such as OCV (high/low) non liner loading, temperature, battery design, battery specification, battery resistance (that initially falls with increased current flow) load time, recovery time and rate, to arrive at our estimated instantaneous CCA value.
The details of the Pico algorithm are proprietary and the results obtained are based on the variables above as accurately as possible, but I do concede the results are not without question.
I hope this information is of some help and brings about some clarity to the results
The image below will help summarize the results: