EEVblog #508 - Can You Test Battery Charge By Dropping It?

Can you determine the charge of an alkaline battery by simply dropping it and see how high it bounces?

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[azy]

The Princeton University team dissected batteries with various degrees of discharge and examined their contents under a scanning electron microscope. They discovered that in the process of discharging, there also a physical as well as chemical change in the nature of the battery.

The zinc oxide forms around the zinc particles embedded in the gel, slowly turning the gel to a ceramic. While the material starts as tightly packed particles, the oxidisation process forms tiny bridges between them, producing a material a bit like a network of linked springs, which gives it bounce.

However, “maximum bounce” is reached when the battery is down to about half its charge, at which point the amount of bounce levels off despite the fact that more zinc oxide is still forming. So the bounce technique can reveal that a battery is not fresh, but it is not an indicator that it’s entirely flat. Still, it’s an easy and instant way of checking the profusion of batteries filling our drawers – no multimeter required.

[bigclivedotcom]

That's bizarre.  I just tried it with two same-brand batteries and it worked a treat.

[bigclivedotcom]

Oh, and remember, those duff batteries can drive a surprising number of LED Xmas lights (the battery operated ones) with a Joule Thief.

[kipkay]

Yea this was never intended to be a scientific test, nothing beats a multimeter or load test for accurate v/amp calculation. It's just kind of a cool and interesting thing. BTW, sometimes devices fail and I can't even count how many times I have taken batteries out of a device to see which is bad or if the gadget is bad.Nice presentation EEVBlog!

[billysgeo]

If you end up actually doing the proper sci test (with the tube and all), you should also do a sound capture and then compare the waveforms. It should be a nice visual representation of the drops.

[MrMonkeykiller]

dont drop them too much the electrons might fall out :)

[nullbewahrer]

Is it possible to use the same method to detect the activity level of used nuclear fuel rods...?

[TravisTerrell]

When I was very young, I was taught to drop AA's on their side, and see whether they flipped. Basically, the same idea, but perhaps more visually noticable than noting the height of the bounce.

[JulianIlett]

What if you tap it? Does the empty battery have a hollower sound?

[ZeroMass]

kipkay lol Instructing kids to assemble class 3b lasers from DVD burners and use without eye protection since 2006 : /

[mdbutler]

A test like this definitely deserves more than a 30 second segment. Glad to see YouTubers test concepts to verify, exactly what the scientific process is about.

[MagnumForce]

Batteries don't change in mass when discharged. The only thing that might leave a battery is electrons, but electrons are so infinitesimally light, that it makes no difference.

What I think is happening is that there is a transfer of mass between the anode and the cathode. The cathode is the negative terminal on a battery. (the flat bottom). In a fully charged battery, the mass is more uniform. But once discharged a majority of the mass from the anode is transferred to the cathode as a result of the chemical reactions that went on in the battery that allowed it to produce electricity.

So this alteration in the distribution of the mass within the battery had a noticeable effect on the bounce. I bet what is happening is that the cathode of the battery is heavier and thus more of the inertia of the battery is transferred into the table allowing more rebound (remember Newton's laws of motion? For every reaction there equal reaction. Since the table is immobile most of the energy of the falling battery is transferred back into the battery with some being absorbed by the material of the table).

The mass of a fully charged battery however is either more uniform or closer to the top/edges and so not as much of the mass gets it's energy transferred. The end result is the bottom of the battery absorbs more of the impact and thus results in the "thud" because the inertia had been absorbed by the cathode material then would have been if the battery was discharged. (cathode not as dense, so it can absorb more impact)


I honestly don't think gas buildup would have any measurable effect on the bounce. These batteries are small. What ever amount of gas they produce is so small, it can't alter the end result. It's more to do with the change in mass of the cathode in relation to the anode.

[TheDenix]

But batteries that are not under load might show wrong readings. Even when I stick them in my device, it, at first, shows that they are full, next few seconds it drops almost all "lines" in battery icon,

[oetken]

What will happen, if you drop the battery on the positive pole? Will the full one bounce harder? It should be, right?

[ChrisWilson]

Have you measured the overall length of one battery, both in a charged and discharged sate, very accurately? I too suspect internal pressure differences. These may show as a slightly elongated case as the negative terminal swells, and regresses very slightly between states.

[XpoZed]

When a battery discharges the negative side starts to bubbling a bit due to the chemical changes inside. So, the bottom part that hits the plot is no longer flat, thus making it "jump" on contact with the hard surface. You can verify that by measuring the batteries with a good caliper or even better with a micrometer.
Of course, that depends on the battery design. In your case, Duracell and Varta are using a positive "body" and a negative "cap", but some other brands are using the opposite.

[CalcProgrammer]

Interesting! I wonder what would happen if you recharged the battery. I've experimented with recharging alkaline batteries at low current (10's of mA) on a bench supply and was able to get them to hold a bit of a charge (enough to run an LED flashlight again after they had died in it). Does recharging the batteries get rid of the bounce, or is the bounce a permanent property after the first discharge? If it's a warped bottom contact it should stay bouncy.

[JaredReabow]

i know why it works, kipkay may have even said, the alkali release gas when they discharge causing the cell to puff ever so slightly, this puff is what causes it to bounce and makes it difficult to stand on end because the rounded puffed end stops it standing and allows it to bounce

[Tedybear]

Have to ask this: What happens if you hooked the "Baterysizer" thing to the dead batteries. Will it then bounce extra high? Or give a larger 'Thud'.... like the sound your wallet will make if you shell out real money for such snake-oil...

[MylesShannon]

A "quick video" for Dave is nearly 10 minutes. I love this guy!