I have been looking to purchase a multimeter for automotive/general usage, but I would like something with a very good min/max function that is capable of measuring the instantaneous max. voltage drop at my 12VDC car battery when under the load of cranking the starter. The overall application of the meter is personal use, so unfortunately the higher end meters like the Fluke in the video below are out of the budget. The Brymen BM-829s has caught my interest because the manual states that their crest function is capable of a 1ms (1000X/s) sampling rate, and the normal min/max function is capable of a 50ms (20X/s) sampling rate. This meter has signifiantly better specs than other similar meters I have looked at such as the UNI-T UT161D, which has a min/max function with a sampling rate of only 333-500ms (2-3X/s). Does the Brymen 1ms crest function work with DC voltage, and would it be fast enough to capture the max. voltage drop in this application? Does anyone have any real world experience using either the Bryman crest or min/max in this application that can provide any further input as to its suitability?
I don't think you need a very fast MIN/MAX function to do this test and it actually might be confusing or yield wrong results if it were too fast. The 13.5ms figure mentioned is from a specification regarding the ability of automotive electronics to operate properly in a worst-case momentary voltage drop during starting and isn't intended as a battery test--and if it is used as a battery test, you need different numbers than given in your video.
Your youtuber is giving you a rough rule-of-thumb method that may work on many modern cars with PM starters and modern electronic engine controls. I don't know where the 9.6 volts comes from, but from experience I can tell you that very early electronic fuel injection cars would sometimes have long crank times because the controllers went offline at ~9.6V and would only come back to life when the engine was spinning fast enough so that the starter load was reduced enough that the battery voltage would come back up. So a 'crank, no-start' complaint would be caused by a weak battery, something unthinkable on older models.
The Fluke 98 Scopemeter had a built in battery test function that would graph out the battery voltage during the startup cycle. I just went out and tried my car, a 2010 Honda Accord I-4 that has been sitting for about a week. The car starts promptly and the battery is known to be good. The initial OCV was 12.41V, which dropped to 11.9 when the ignition was turned on. Ambient temp is 64F after an overnight low of ~56F. I'm sorry the picture isn't better, but the backlight is weak on the 30-year old Scopemeter and although I have the FlukeView software and cable, it hasn't worked since Windows 95. As you can see, the voltage briefly drops way below 9.6V, but then pops back up to 10V+ right away.
A Fluke 27 using MIN/MAX gives a MIN of 10.19 volts and a MAX of 14.05 which indicates a good battery and a good charging system according to the test mentioned--both of which are correct results. That might be a good meter to start with for your usage, or if you are really interested in automotive, start scouring eBay looking for a Fluke 98.
