What the fine posters are neglecting with the voltmeter is that a standard (aka, Harbor Freight <$7) voltmeter can only measure the surface charge of any source without performing another test.
In order to get a true voltage measurement of a storage cell, you will have to do a load test. To perform a load test, you need to measure the voltage before AND after the cell is placed across a known load for a specified period time. This, then, allows you to measure the absorption charge - which is the actual usable charge of the cell. A significant difference or a reading below acceptable (in this case less than 1.5V) indicates a discharged or “dead” battery.
I’m not going to waste time interwebbing for information about whether the density of the media is lesser or greater after discharge but, astoundingly, both explanations could be valid and are very well presented. :smack: I can’t believe I joined this group only to post here.
I did a quick experiment with four batteries: two charged, two discharged. The brand was the same. All batteries were clean and visually indistinguishable (the discharged ones were from a device that I installed fresh cells in, and accidentally left running all night). They were all from the same batch.
I weighed them with a scale capable of 0.1 g precision. No difference to speak of.
I shuffled them by shaking them in my cupped hands with my eyes closed, and then sorted them into charged and uncharged piles by bouncing them in pairs. The difference was unmistakable. I verified that I had gotten it right with a voltmeter. I repeated and the results were the same.
Not quite up to scientific standards for blinding and statistical certainty, but I’d definitely say the effect is confirmed.
Hi Khoa,
You are correct. I made an error in my original calculation. The correct calculation shows the total volume of the reactants in the battery does decrease rather than increase but by 39%.
However the volume of the anode at the center increases, because oxidation of the suspended Zn particles to ZnO takes up about 45% more space.
Here is a table which shows my calculation.
molecular wieght Density volume/mole "#0f Moles
Zn 65.38 7.14 9.15686274509804 1
MnO2 86.937 5.026 17.2974532431357 2
total vol 43.7517692313694
ZnO 81.408 5.606 14.5215840171245 1
Mn2O3 157.8743 9.53 16.5660335781742 1
total vol 31.0876175952987
This should make the center more solid and less jelly like. A friend cross sectioned the spent and fresh batteries with a hacksaw and verified this.
Note to the newb: “Quetions” is not a typo. A quetion is a virtual particle representing the quantum unit of entropy, which is inversely related to information. I.e., a quetion is the basic unit of not knowing something.
This is compelling and argues against my impression of the original assertion. That is, I thought, “Hell, if used batteries don’t bounce or they bounce noticeably differently from fresh ones, surely someone would have noticed that by now. That factoid should be part of the common wisdom at this point.” But, now I’m thinking, maybe not.
Looking back at my original calculation, I used a density of 4.5gm/cm3. The above calculation used a density of 9.53gm/cm3, which I got from Wikipedia. Searching the internet, I find that most of the web sites describing the properties of Mn2O3 give the densisty a value of 4.5gm/cm3. This means that my original calculation, which showed a slight increase in total volume for the spent battery is correct.
