Testing batteries

I don't have time to go into excruciating detail, but an alkaline cell's condition is largely indicated by its unloaded voltage. Just sort them by voltage.

This is not true of carbon-zinc cells, but you rarely see them these days.

The short circuit current is a nice indication of charge left. I test them with a multimeter at 20 amp range, and sometimes compare with a full(new) battery.

It depends a little on what use you will make of the used batteries. I would suggest a 10 to 20 ohm resistor, that will load the battery to between 50 and 100 Milliamperes (ma), which is a reasonable load. I would look for an output of at least 1.25 volts at that range. Try a pair of lw-edge batteries After you have tested a few, and try them in your proposed application and see how they work. If ok, then you can use all batteries that meet that voltage level. If they are too weak, select a pair from a higher range and try those, until yuo find the minimum test voltage that cells meet the then work ok in your application. Or, just try them in a flashlight and see if they are bright enuf. That's what I do when I am too lazy to break out my voltmeter.