The key thing is what it is not - a simple voltmeter measuring the
off-load voltage produced by the cell.
These testers have a built-in load resistor and give an indication of
the voltage that the cell will produce when powering equipment.
Some testers (not this one) draw a great deal of current when used -
testing too often and for too long can substantially reduce battery life!
Radio Shack do have a web page that discusses testing batteries:
Which only shows why you shouldn't go to Radio Shack for technical advice ;)
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