Today I learned that a battery can experience a voltage reversal. I never heard of this before.
The background: there is some device in our fridge which starts to play a melody once the door is open for too long.
The device is operated using 3 Alkaline AA Ikea batteries (ALKALISK, 1.5V LR6 AA AM3 MN1500 - 23050).
All batteries in series connected produce 0.8V ... so I though they are all almost empty.
I was more than surprised to measure that the first and the second battery have got 0.8V, and the third has got -0.8 V (yes, minus 0.8V) !
According to Wikipedia this may happen to re-chargable cells:
"when a battery made of several cells connected in series is deeply discharged. The problem occurs due to the different cells in a battery having slightly different capacities. When one cell reaches discharge level ahead of the rest, the remaining cells will force the current through the discharged cell."
Also, I can see some little bulge on the discharged battery - an indication of a chemical reaction.
I didn't find a hint this can happen to Alkaline batteries. Interesting.
The picture has been shared under CC BY-SA 3.0 license. Source.