Bill in Co. said:
Interesting - thanks.
But is this because they weren't available in the identical size packages,
with the same electrical capacity (i.e., voltage, ma-hrs, etc)? Or
because of the external charging circuitry (if any) possibly having
different requirements?
Although the electrical characteristics are pretty similar (apart from the
greatly increased mAh capacity), Ni-MH has an exothermic charge reaction
(Ni-Cd was endothermic). This means that when rapid charging the cells, it
is necessary to have temperature monitoring and cutout which was unnecesary
with Ni-Cd. However, a temperature sensor could be used to detect the end
of charge condition for Ni-Cd (as the charge power had to be disipated as
heat once the battery stopped absorbing it's charge). This cannot be so
easily done in Ni-MH as the cells get warm anyway.