Eric Pederson wrote:
[snip]
> My vague understanding is that self discharge is unlikely to lead to cell
> reversal -- unless the cells are in a unit which actually draws current,
> in which case this is not really self discharge (nor storage). If you
> have more indication that this is not true (including personal experience)
> please let me/us know further. I have a lawnmower at 24V with a sealed
> battery pack which I have been leaving in a depleted state after each use.
> I just charged it this weekend after its second winter in a depleted
> state, so I guess I'll know soon!!!
A few things to keep in mind about cells and batteries: a cell is a
single internal unit that supplies 1+ volts ... and a battery is a
groups of cells connected in series to supply 3, 6, 9, etc. volts.
That's why it's called a battery ... meaning a group, as in a battery
of artillery. Self-discharge can NOT result in cell reversal ... the
battery discharges to zero, but does NOT start to self-charge with the
opposite polarity. Cell reversal occurs in batteries (a group of cells
connected in series) when the battery is deeply discharged and there is
one (or more) weak cells. The weak cell reaches zero charge, and then
the continued current flow from the remaining strong cells causes the
weak cell to begin to charge with reversed polarity. That is why a
single cell can be discharged to zero voltage with no damage, but a
battery should NOT be discharged past the point where the voltage is
less than 0.8 volts per cell. For good practical information about
charging and discharging NiCd batteries, visit a hobby shop that
specializes in battery powered radio controlled models ... racing
cars, trucks, airplanes, or boats.
-Nick T.
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