Here's a YT video by Duracell about how many batteries declared dead and sent to recycling still have some usable energy. In the beginning of the video there's a sequence where they have a row of batteries and a person quickly touches each with a pair of probes to decide whether a battery is worth anything.
The measurement procedure is not documented, but I'd guess they just measure voltage on the terminals. Batteries have likely been idle for days or weeks before the measurement.
Suppose I want to do a similar project and have a pile of batteries and a voltmeter.
What's a reasonable voltage threshold to decide usable alkaline batteries from useless ones?