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I have asked this question on EE SE but could not get a satisfactory enough answer.

I have shorted an AA battery through an ammeter. Inititially, the current reading on ammeter was around 0.9 amperes but it quickly and stedily decreased in time over a period of 10-15 seconds.

I thought that the reason for the steady drop in current is due to a steady drop in voltage when I was shorting the battery. I have reached this conclusion because after breaking the short, I have measured the voltage of the battery and observed that the voltage is "replenishing" steadily at a rate of approximately 2-3mV/sec.

So I am wondering why did I observe such behavior? Why does the voltage over the battery drops steadily on high currents? Also, why does the battery's voltage replenish after breaking the short? What goes on behind the scenes?

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  • $\begingroup$ Ideally I would expect a sudden decrease to 0 when shorted and a sudden increase to $V$ when open, may be this has something to do with chemical reactions inside $\endgroup$
    – Courage
    Commented Dec 26, 2015 at 16:21
  • $\begingroup$ Should I better ask this question on chemistry SE? $\endgroup$
    – Utku
    Commented Dec 26, 2015 at 16:23
  • $\begingroup$ You could try that, or may be an expert probably could answer it here $\endgroup$
    – Courage
    Commented Dec 26, 2015 at 16:28

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I thought that the reason for the steady drop in current is due to a steady drop in voltage when I was shorting the battery.

When you 'short' the battery with the ammeter, the battery voltage becomes effectively zero volts. This is because an ammeter has very low resistance between its terminals. You're essentially measuring the short-circuit (zero voltage) current capability of the battery. You can verify this by placing a voltmeter across the battery terminals in addition to the ammeter.

Inititially, the current reading on ammeter was around 0.9 amperes but it quickly and stedily decreased in time over a period of 10-15 seconds.

It is likely that your battery is not fresh (fully charged). Looking at the chart below, note that all AA batteries tested supplied 2A into a constant current load for at least 15 minutes.

Thus, a fresh AA battery should be able to initially deliver considerably more than 2A short-circuit current. Note that the large short-circuit current will heat the battery while rapidly exhausting the reactants within.

enter image description here

Also, why does the battery's voltage replenish after breaking the short?

Essentially a duplicate of Why do batteries recover after a load is removed?

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