I just tested my car battery using this method.
The battery is good.
The kitchen tiles are fucked.

I test them licking the ends with my tongue

R.I.P Duracell

He would better prove his point if he compared an Energizer to an Energizer.

#4 That's Duracellist I tried it with a couple of watch batteries works really well except the little barstuards (subsidiary of Duracell) bounced off the table and the cat got them, now I've got a $6780 vet bill for battery extraction. The extraction was only $370 but she also needed a cat scan which was $1240 and it was a mobile cat scanner and the battery went flat so I told them about the battery testing method and we tried it and the battery was flat and it bounced off the table and wrote off a smart car. you will be hearing from my attorney.

Learning everyday!

A used battery tend to get a bulge on the negative side. If said battery is still in a device it'll eventually leak, might even leak by itself eventually just lying around.

#2 must be popular with the ladies with that extra long tongue

(gotta connect both ends with tongue to test that way)

I've been doing this for years now.

#10 What smiling while wearing a tie? I've done it wearing a teeshirt and sometimes wearing nothing at all. Sometimes I do it when I'm sad just to confuse the other inmates

#9 No you do not. That's not how you test the battery with your tongue.

#1 Your car battery is an alkaline dry cell?

I can imagine this idea works since fresh batteries have some ammount of liquid acid inside which moves slower than the body when dropped. that could act like a shock absorber after impact which can causes the battery not to bounce.

Like someone noted already, the battery needs to be really old for this to work. While all the batteries are made in similar manner, small changes in stamping presses can make the negative side bulge when new. So you need to compare against the same brand, type and even month when manufactured. Old batteries tend to bulge on the negative terminal but it needs to be at least a year old. You batteries in your remote might show the difference. In any case, outside differences in batteries is NOT 100% sure way to determine how the insides are still performing.

#1 You should be a radio ham

There is no basis for this to work. I've tried it with batteries BEFORE I TEST THEM and you could not tell anything. The important part is to try this BEFORE you know if it's good or bad and you will see it does not work. I think he dropped them a little differently since he already knew which one was good.