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Did you know that a Ni-Cad cell gets colder as it charges before it is fully charged?
But a Ni-MH cell gets warmer and warmer as it charges. Try feeling them when they are both are charging.
Therefore if the Ni-mH cell is charged at a current that is too high for it then it gets too hot. With too much charging current a Ni-Cad cell begins to get warm due to its resistance dissipating heat.
When both types of cells are fully charged then their rise in temperature and rise in internal pressure depends on the amount of over-charging current.
The "peak" of a Ni-Cad cell is much more than the peak of a Ni-MH cell so the Ni-Cad charger will over-charge a Ni-MH cell and will miss seeing its peak.