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.

 

[oil pan 4]

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.

Its not the battery tester. Im sure the battery would be fine if it was in a straight gas car.
The problem is battery and hybrid car electrical engineers the term "12v" too literally.
If the battery hits some arbitrary number say 10v during start up it can cause problems.
In a straight gas car a battery hitting 10v is perfectly fine, straight gas cars and trucks usually don't start having starting problems till you start hitting like 7 or 8 volts and that's what the battery testers are looking for.