Battery tester accuracy?

[nthach]

My dad had the aux battery in a 2017 Prius die a few times, he keeps a jump pack with him. AAA came out to give him a jump but their Midtronics tester said the battery is weak/in need of replacement. I’ve tested it with a Topdon BT101 and it said good battery. Is there something special the Midtronics has that the Chinesium tools don’t?

The car is a cab, so there is aftermarket “unfitting” done, wiring for a cheap Android tablet, POS receipt printer/PIN pad and a dashcam so there’s some parasitic load that doesn’t go to “normal” sleep. I’ll have to put a DMM on it to do a check. He wanted me to put in a new battery - Costco didn’t have a H4/40 battery in stock. I decided to install a Deka flooded battery from the local parts house. Made in Austria, Walmart was $20 more expensive.

 

[charbaby]

IDK so this is of no help or answer to your question.

I typically do my parts shopping shop at AAP. So now & again I’ll stop in to have my older car batteries tested for free. Usually the batteries show to be in good shape.

Then I will drive directly across the street to AZ and have them do the same. At AZ, the same battery, same day, the battery almost always show to need a replacement.

Often, I’ll go to AZ first then to AAP and the results are the same…Just saying!

 

[nthach]

IDK so this is of no help or answer to your question.

I typically do my parts shopping shop at AAP. So now & again I’ll stop in to have my older car batteries tested for free. Usually the batteries show to be in good shape.

Then I will drive directly across the street to AZ and have them do the same. At AZ, the same battery, same day, the battery almost always show to need a replacement.

Often, I’ll go to AZ first then to AAP and the results are the same…Just saying!

Why didn’t I think of that? They all seem to use the same Midtronics tester - and those are OEM validated as tools for dealership work too.

The new Deka has been in for almost a week. No issues.

 

[SC Maintenance]

I have a cheap Ancel. Generically the "good battery" is based on some number of variables, so its possible there tester used a different threshold than yours. Either way I don't find this metric compelling.

I am usually looking for a battery that gets pretty close - like 80%, of rated cranking amps when charged fully then left to rest for a couple hours. I also want internal resistance to be below 10 milliohms. If not I would replace the battery.

The "good battery" on mine can be highly influenced by state of charge.

 

[martinq]

IDK so this is of no help or answer to your question.

I typically do my parts shopping shop at AAP. So now & again I’ll stop in to have my older car batteries tested for free. Usually the batteries show to be in good shape.

Then I will drive directly across the street to AZ and have them do the same. At AZ, the same battery, same day, the battery almost always show to need a replacement.

Often, I’ll go to AZ first then to AAP and the results are the same…Just saying!

Maybe that AAP is using a load tester that's bringing the battery just below the "pass" threshold of the AZ tester.