When the nickel-cadmium battery was first developed, it had serious problems with 'memory', due which it would only deliver as much energy as was called upon in past discharges. But this is a thing of the past, and the modern nickel-cadmium battery has been redesigned to not suffer from this fault.
However, the original fault of memory has been replaced with an equally disastrous fault, and that is crystalline formation within the battery.
After extensive use, crystal formations occur on the negative plate of the nickel-cadmium battery.
These crystalline formations reduce the amount of energy that can be conducted by the plate, by reducing the active surface of area that is available. This reduces the performance of the battery, but if this were all it would not have been too serious.
But what actually occurs is that the crystalline formations grow larger and larger until they actually pierce the insulating barrier between the plates, and can touch the positive plate. When this happens, the battery shorts out and cannot be reconditioned.
Generally speaking, these crystalline formations occur when a person doesn't know how to charge and discharge a nickel-cadmium battery properly.
As a matter of fact, incorrect charging is at the root of most problems with most kinds of batteries. Each kind of battery has an optimum method of charging and discharge, and if you keep to this method you will massively increase the life of that particular kind of battery.
In the case of a nickel-cadmium battery, it is extremely bad for the battery to bring it repeatedly to full charge without doing a complete discharge of the battery.
Many people, for example, will note that their battery has fallen to half its charge and put it into the charger to bring it up to full charge.
In the case of a lithium-ion battery, this is actually a good practice.
A lithium-ion battery lasts a great deal longer if you never allow its charge to fall below seventy percent. But, what works in the case of a lithium-ion does not at all work in the case of a nickel-cadmium.
In the case of a nickel-cadmium battery, if you were to regularly bring the battery up to full charge whenever it fell to seventy percent or so, you would end up destroying the battery.
What you need to do in the case of a nickel-cadmium is to completely drain the battery periodically under a light load.
Attaching the battery to a flash light until the light goes off is an excellent way to completely drain the energy from the battery. Now, you can charge the battery to a hundred percent, and it will work perfectly well.
Please note that this charge-discharge cycle does not need to be done too often, as doing so will also degrade the battery. It is suggested that you do a charge-discharge cycle no more than four times a year.
What is important, however, is that if your battery goes for half a year without a complete charge-discharge cycle, the crystals that are formed may harden and then become impossible to remove, making the battery exceedingly resistant to reconditioning. It can still be reconditioned, but then that requires a more specialized process.