What does a battery tester measure?

I have an inexpensive Radio Shack battery tester. This one ...
http://rsk.imageg.net/graphics/product_images/pRS1C-2265632w345.jpg
(except that the needle rests at the bottom of the red - dead zone until a battery is inserted.)
What does a device like this measure? Volts? Or something else?
Thanks.
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Just A Guy wrote:

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:
http://support.radioshack.com/support_tutorials/batteries/batgd-B08.htm
Which only shows why you shouldn't go to Radio Shack for technical advice ;)
-- Sue
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snipped-for-privacy@webtv.net says...

Volts, under some load.
--
Keith

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