Why a dead alkaline battery bounces!

The simplicity of science - observations, hypotheses, repeatable tests - rears its gorgeous head in this video.

In today's episode of science, an observation is taken that fresh, charged batteries don't bounce. In fancier language, they have a very low coefficient of restitution. Old, discharged batteries, on the other hand, bounce just fine. They have a much higher coefficient of restitution - not like a full one or anything, just higher. Hence our first step: observation.

So the narrator of today's video makes a couple of hypotheses: gas build up (increasing pressure) or gel build up (damping the bounce).

Then we get to the repeatable tests. He builds a nice, little set-up to drop the batteries consistently ensuring that the observations are real and consistent. The set-up gets modified a bit to instead drop a piece of brass onto the different batteries. One hypothesis (the gas build up) finds itself on shaky ground. A further test - drilling into the batteries to allow any pressure to be relieved - fairly well dispells the hypothesis entirely.

So, the narrator cuts the batteries in half (I hope he wore goggles) and sees the change in the discharged batteries. I particularly like the analogy to the dead blow hammer as it relates to the gel-filled, new, un-discharged battery.