It's a test that claims you can tell a dead battery from a good battery by dropping them on their negative end onto a hard surface. A dead battery will bounce, a good battery will land with a solid thud without bouncing.
Seems plausible enough I suppose. A fresh battery still has the two chemicals segregated, so maybe the negative end is more dense than it will be after the battery has discharged. I think the electrolyte also hardens on a discharged battery, which might explain the difference in bounce. I'm going to test it out later
