When using these modern battery testers, the terminals must be clean and snug. And the tester only provides valid data when connected right at the battery right on the connector is good enough, or better would be right on the battery terminals.
Some vehicles have batteries in hidden away locations with jump post under the hood someplace. You can not get any accurate reading with these modern battery testers at those jump post. Theres too much wire between them and the battery.
These testers use changes of battery voltage at more than one loading of the battery to accurately calculate the internal resistance of the battery. This is in milli-Ohms. That thousanths of Ohms. Such as if it says 3.2 milli-Ohms, that is 3.2 / 1000 of an Ohm.
The wire between a battery and remote jump points adds enough additiinnal resistance to the circuit that theres no way these testers can read a battery from those locations.
These testers work great if used at the battery post or on the connections at the battery if the connections are clean and snug.
Just dont even try to use them on remote jump locations.
I like my tester, and use it often. It caught a few batteries ready to fail and saved friends and family from no-starts.
One family member decided to not listen, and did not replace their battery when I told them to. When it failed a few months later, it unfortunately started a domino effect that cost a heck of a lot both in money and down time of the vehicle. It was a 2007 Altima hybrid. When the battery could not keep the voltage high enough during a cold winter morning start, the spark was too weak, sparkplugs got wet with fuel, that loaded down the coils, one failed. It has an uncommon 12 Volt size AGM battery. It took several days to get. When put it, it would not start. Got an appointment at a dealer and had it towed there. Backing it up ramp at dealer lot entrance, tow truck driver kept front of it too high and caught exhaust and destroyed tailpipe and muffler destroying both. Only one mechanic at dealer who's qualified to work on hybrids, and he's booked up, so had to wait a week for him to find and fix bad ignition coil. Then had to wait for dealer to fix exhaust and tow company pay for it.
All in all, battery + $400.00 to diagnose and fix bad coil. AAA for tow. Tow company paid for exhaust, but getting it fixed added more days to down time. Vehicle was not available for 2 weeks while this all plaid out. And all because someone wanted to save a few dollars by not replacing a battery that tested bad but still started the vehicle, just to squeeze two more months use out of it before buying a new one.
Yous pays your money, yous make your choice.
I place high value on reliabality. So, test and replace when indicated.
BTW, one 51R flooded 12 volt wet battery that was rated for 500 CCA for a 2018 CRV, tested 508 CCA when it was exactly 60 months old on a cool day. It failed as a short two weeks later. It was in a 2018 CRV so 500 CCA was plenty enough. But when it failed as a short, even a charged up 1,000 Amp NOCO jump pack properly connected could not start it while that internal shorted failed battery was still connected. That NOCO was only one year old and it was charged up. At least that jump pack was smart enough to not cause the battery to explode.
^ This is why I now draw the line at 1.1 X Rated CCA. if it's below that, it gets replaced.