> If "...always used each battery until it was drained..."
> means you ran the drill till it stopped or nearly so, you're
> probably killing the packs.
Exactly so. The supposed need to drain NiCad batteries completely for long
life is basically a myth; a misunderstanding of the "memory effect" that got
a lot of press time many years ago. Unless you are putting a satellite in
orbit (so it gets sunlight/charge current for exactly the same amount of
time each day, followed by exactly the same discharge each day); AND have a
circuit that shuts things down if the voltage dips just a little below
normal; then the "memory effect" can safely be ignored.
Any voltage reversal on a NiCad dry cell will cause a (tiny) short between
the plates. The short may or may not self-heal when the cell is charged the
right way, but as Karl notes, it will eventually stay shorted. Sometimes
you can forcibly burn the short away, but since you are literally burning a
hole in the plate, the capacity will be reduced (meaning that cell is even
more likely to short the next time). Eventually of course, there is no
capacity left.
Randall
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