Thanks for the detailed explanation from "kennybobby".
To use what I have on hand and experiment with a 4-wire setup, I will connect two wires to each end of the battery (one wire for voltage sensing to a meter and one wire for current flow through a load) but to simplify the setup, I will connect the two wires at each end of the battery to only one robust terminal at each end of the battery. I will use a normally-open momentary switch in the wire carrying the current and a clamping ammeter over this wire to measure the current. I have two Uni-T UT210E meters that should work for this setup.
I have no reason for doing this except as an interesting hobby that is also an educational experience. Analyzing chargers satisfy my needs for testing battery capacity but I would like to find something that is more consistent for measuring battery internal resistance.
I will eventually purchase one of the YR1030 style Battery Internal Resistance Testers after I better understand the differences between "battery internal impedance" and "battery internal resistance" and are also able to decide which of the various offerings would be the best one to have (cost versus accuracy versus usefulness).
I recently purchased a Uni-T UT383S Lux meter to calculate Candela and ANSI Throw and will be experimenting with attempting to measure Lumens in a home-built semi-integrating Styrofoam Cooler and Plumbing Tube. If I was more computer oriented, I would try using programs to save and display results but quick and easy stand-alone devices give me adequate pleasure for less effort. I do wish I had a precision adjustable bench power supply to easily check lights for Low Voltage Protection and on Anduril lights to check the accuracy of the light's voltage readout.