If there is any truth to this at all (a point I am not yet willing to stipulate), it could also be due to differences in the batteries initially. The battery companies are always slightly tweaking their designs and compositions, to try to eke out that slight edge over their competitors. It might be that, due to these continual changes, the batteries made last year have different elasticity than those made this year. And of course, a battery made this year is much more likely to still be full than one made last year. This is another good reason to perform Machine Elf’s test.
From the patent’s own abstract:
[QUOTE=US Patent 5567541]
since the masses of the materials do not change considerably, the total volume occupied by at least one of the electrodes will change
[/QUOTE]
In other words, they are relying on the volume to change.
Yes, prior art may involve single cell batteries. But that has nothing to do with patent you cite, which involves physical measurements of a change in volume - which do not occur in this particular case for a single cell.
That is, unless you have a way of extracting the electrodes from the cell, which defeats the purpose of a bounce test in the first place.
Prior art doesn’t mean the new patent is applicable to that prior art.
As I noted, you have nothing that indicates you controlled for confirmation bias, and we’re taking your word that the cells were “otherwise identical”.
It’s great as an anecdote. It might even be Mythbusters level good. But it’s not quite there as actual, reliable evidence.
With a smile, I’ll admit, but at least they’d surely control the experiment, weigh the cells, and film and time the bounce with a high speed camera. Of course the new “bounce method” is on the web now, so it’s too late to patent it.
As a battery discharges, where could be a chemical change in the interior contents, which would change the amount of pressure exerted from the inside on the rigid casing. A battery will bounce higher if there is more internal pressure, like a golf ball, even if the weight remains consant.
I just tested some batteries by tapping on the side of them with a spoon. The good, fresh batteries made a dulll thud. The older batteries made a distinctly ringing sound when tapped with the same spoon. Tapping on the end of the battery showed no difference, but tapping on the side made a very distinct difference of sound pitch and reverberation. Which suggests to me that with age and usages, the chemical reaction inside the battery expands the pressure of the components inside.
The sound tapping method seems to me to be much more reliable and easier to control the test conditions and observe the result…
Beware of bias due to lack of blinding.
If you really need to know the condition of a battery, invest in a voltmeter.
I think someone saw how the density (specific gravity) of the electrolyte in lead-acid batteries changes with charge state, and tried to apply it to other battery chemistries.
If someone has a test procedure, I have access to very, very accurate balances and will carry it out.
I could probably weigh a AA battery to certainly 5, maybe 6 grams places.
But I don’t think there will be a difference.
I happen to have some well-discharged AA batteries awaiting disposal, and some brand new ones awaiting a call to duty. So I weighed these, and did the suggested bounce test.
No differences are noticeable.
My scale is accurate to 1 gm and the batteries weigh 24 gm, so the resolution there is not amazingly good. And I’m not sure how to precisely quantify the bounce test. But I can definitely report that I lack the ability to distinguish between charged and discharged using this method.
Sorry for the self quoting here but I was thinking about this and it seems the best would be to compare individual cells new from the package and then run them down to nothing to get the greatest change in mass.
I can do this.
Wouldn’t 120v incandescent bulb be a good load to discharge a 1.5v cell quickly and reliably?
at the amount of mass that might have to be measured you will have trouble with dirt, grease and the material change (loss of package material) when you bounce the battery.
a 120V bulb would not be a good load to discharged a 1.5V cell at all.
Yes, you will need to devise a cleaning regimen that leads to a reproducible mass, without removing too much material from the battery.
Maybe clean both used and unused batteries?
Well ideally you should get the same mass every time after cleaning. Also, if you’re going to go to 0.1 mg, the natural variation in batteries’ mass is probably greater than the effect of charge.
I took a Ohm meter to a 60 Watt incandescent bulb, and got about 18 Ohms. That would give 83 mAmps, and to discharge a 2500 mAhour battery would take about 30 hours. So no, probably not what was meant by “quick”.
Check out the Wikipedia entry on Alkaline Battery:
http://en.wikipedia.org/wiki/Alkaline_battery
And in particular, importantly, the cross section diagram:
http://en.wikipedia.org/wiki/File:Alkaline-battery-english.svg
There’s a cavity at the bottom with a pressure expansion seal in the middle. It’s there because the battery manufacturers know the total volume of the anode and cathode above it are going to shrink during discharge and they can’t allow that shrinkage to pull the cell apart. Also, because of the pressure seal, nothing enters the cell and nothing leaves, so the total mass and hence the weight don’t necessarily change with discharge unless the seal bursts.
The half reactions show the electron flow electrochemically and through the discharge circuit. The overall reaction shows that after discharging, oxygen ions have moved from the Manganese Oxide cathode and into the Zinc Anode, which becomes Zinc Oxide.
No oxygen enters or leaves the cell, but the oxygen* doesn’t occupy the same volume* when originally part of the Manganese Oxide and thereafter as part of the Zinc oxide. It depends on the “intercalation,” or in ordinary language, how well the oxygen “fits” in between the other atoms in the cathode and then the anode.
In this case, the oxygen fits better and occupies less volume as part of the Zinc anode than it did as part of the Manganese Oxide cathode, so the *total *volume shrinks ever so slightly, the cavity at the bottom grows ever so slightly, and the bottom of the can becomes ever so slightly more elastic.
The difference is barely large enough to see in an iPhone video, but can be measured in its sound track. When new, at 1.60V, a cell bounces from a 5" fall about a half inch off a granite surface then falls on its side with the two peaks in the sound track about 150mS apart; when discharged to 1.40V, the same cell bounces about an inch and the time is closer to 200mS.
I thought for reproducibility by my science peers, we should use a load that everyone has readily available. And sure, quick is relative but a bulb is certainly quicker than a lot of devices that typically use AA batts. A resistive bulb would also be best to ensure the battery is fully discharged.
Any better ideas for a load?
It would be a good load for ensuring that the battery is discharged, however it gets there. A new battery connected to the light bulb should put about 1.5 Volts across it. A discharged battery will have a smaller voltage. Just make sure your battery can only put 0.1 Volts or less across a 60W bulb (or whatever voltage threshold you want to use), and you’ll be sure everyone’s on the same page for what counts as a discharged battery.
Rather than shrinking, the reacted contents have expanded.
The solid material in the anode, Zn, expands by about 50% when it is oxidized to ZnO during the reaction and the total reacted materials expand by about 10%. This would make the pressure in the battery go up. My volume calculation is based on the density and molecular weights of the materials.
Fresh battery materials ( 1 mole Zn and 2 Moles MnO2)
Center + Outside = total
Zn + 2MnO2
9.951+34.552 = 44.504cm3
Spent battery
ZnO + Mn2O3
14.456+ 35.082= 49.538cm3
A friend of mine sawed a spent and fresh battery in half. He was able to extrude the mixture of Zn powder and gel from the center anode of the cut fresh battery, which didn’t bounce. He found the center of the spent battery, which bounced was a more solid material which could not be extruded by pressure from the pliers.
It could be that the expanded particles in the center of a spent tend to form a more solid matrix touching one another. They do not float and jiggle around inside the gel and dissipate the energy of impact, like the smaller particles in the fresh battery.
I am sure weight cannot change unless system is an open system. Only change in weight would be nuclear reaction.
I did the same calculation as you using wikipedia equations. I found that density went down by about 12%.
I did a bit of experimenting with 5 different batteries about 5 drops each. All alkalines from 3 different brands (one kirkland, one hitahi maxell, 2 duracell procell and one duracell). They all bounced differently from time to time, if my angle or the way my fingers released the battery changed. I was sure when doing the test that 3 of them were good and 2 of them were dead. Then I used the voltmeter. They were all good!. Some had slightly higher voltage. And 2 of them that I was sure were dead in fact had higher voltage.
So, I am not even sure this works. I am not sure that less dense batteries should bounce more.