From FB group
Another FB member, who’s not in the groups, has also built a battery capacity tester. I think he uses a 10 ohm resistor. The typical testers found online apparently use what the battery makers say they use in the data sheets.
This link is for the .PDF of the apps manual for Eveready Alkaline AA cells.
http://data.energizer.com/PDFs/alkaline_appman.pdf
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BTW, IIRC, the battery capacity tester this member built uses an Arduino to monitor the battery voltage as it is discharged, and the times and voltages are logged to a file of values in CSV format, which are later imported into a spreadsheet. I believe the Arduino only switches the discharge on or off, it doesn’t control the discharge current.