Interesting topic being we have both a fancy hand held digital battery tester at work and a old style heavy resistance type.
Last week I was doing a 750 watt inverter install on our service truck , 2012 Ford F350 diesel, and figured I would do a battery test being we had had a few issues with the batteries running down way sooner than expected for the given load they had when on site.
Interesting thing was the digital unit gave both batteries a good rating of 90% plus, based on what I don't know being the test takes about half a second using 14 ga leads, whereas the old heavy high current one requires a load test of some 20 seconds at about 200 or so amps to get a reading.
According to that both batteries barely passed as Okay falling right on the bottom line at 20 seconds and failed at 25.
The general consensus of the shop guys no one trusts the new digital unit being it has let too many questionable batteries go out to site where they failed a short time later yet the old high load long duration tester has yet to miss diagnosis a weak battery.
BTW the truck battery issue came down to weak batteries and one battery likely not being connected at all due to considerable terminal and cable corrosion. This week the guys say it never gave them a bit of trouble and seems to start better now as well even though the batteries are at the bottom end of their service life.