Many a time I have fetched the big box labelled "electrical repair" and set up the big meter, just to test a battery. If only I had known about these. Press the ends either side of the battery (any 1.5 volt cell, e.g. watch battery / button battery) and if the battery is good the entire end of the tweezers light up. So simple!
To download an instruction manual for all models of battery tester.