>The battery packs are made up of 1.2V Nicad cells. But if the cells are
>discharged, it is not just a case of measuring the voltage.

Sure, Quentin.

The basic chemistry determines voltage.  A NiCd with no load on it, unless
_very_ dead, will register around 1.2V.  All they do is a no-load volt test.

Some of the smarter units will apply a small charging current to it for a
short duration, then measure the pack to determine cell count before
starting charge.

Even smarter ones will continuously monitor cell voltage.

Note that a fully-peak-charged NiCd can exceed 1.2V by quite a bit, so as
the cell count gets above 7 cells, these chargers become less accurate as
charge approaches full.

The real issue though is that they charge with the correct current.  NiCd
cells like constant current charging, not constant voltage (like lead-acid
cells).

Andy

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Andy Kunz               Life is what we do to prepare for Eternity
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