You need to either try it in another appliance to see if it works or use a button battery tester like the one at http://www.amazon.com/Watch-Battery-Tester-Button-Cell/dp/B000OVHUHG which tests the most common batteries including button type.
The battery tester is the best way of checking as it will let you know how full the battery is so you can judge how long its likely to last.
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