On 12/19/11 2:13 PM, William Sommerwerck wrote:
It's called "cell reversal". It's most-common with rechargeable devices
using nicad or NiMH cells, but I also saw it in an HP calculator that used
alkaline N cells.

Here's what happens... One of the cells has significantly lower capacity
than the others. When it hits zero volts, the other cells are pumping
current through it /in reverse/. This causes the cell to charge up
backwards, with reversed polarity.



Thanks William and Dave for the explanation.

I had saved the two alkaline batteries that I pulled about 10 days ago
and just retested them. One was still weak, the other (presumably the
one with the reversed polarity) is stone cold dead.