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NiCd batteries can indeed be rejuvenated, though I've not heard of the 'night in a freezer' solution. In many instances the decline in NiCd performance is due to the creation of dendrites within each cell of the battery. These can be burned off by a very short burst of over-voltage and high current. Dendrites, in effect, produce a leakage current path which precludes a battery pack from charging to its normal capacity.
I have used this method with good results. In my case I have used a 30 volt transformer with a three ampere (peak) capacity. The batteries treated in this manner varied from 4.8 volts to 9.6 volts (i.e. four to eight cells). The idea is to connect either the negative or positive of the transformer/power supply to its mate on the battery. The other pole of the transformer is then 'flashed' across the other battery terminal. I usually 'flash' two or three times with a few seconds between each.
You might see a spark as you flick the free wire across the battery terminal - but if you do not don't worry. Whatever you do, don't hold the two connections on together.
It is not guaranteed to work (after all a dead battery is a dead battery) but it certainly does so more often that it does not.
Oh yes: Don't do this with an SLA battery.
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