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Memory Effect 3

The Ni-Cad memory effect business is an urban myth, but it still keeps coming up. In summary, if you overcharge a Ni-Cad battery, it develops a voltage depression which makes the battery appear to go flat earlier than you would expect. Since the discharge curve is so steep, sensitive devices which rely on battery voltage to detect when it is almost flat, will report that it is almost flat early due to the voltage depression, when in fact the cell still has significant charge. The voltage depression can be rectified by discharging the cell to its full discharge level.

Many people misinterpret this phenomenon and conclude that the battery somehow remembers its last discharge level on the next charging cycle. This is not the case. The only effect that the current charge level has on the next charging cycle is that it's much easier to overcharge a Ni-Cad cell whose current charge state is unknown, than it is to overcharge one which is known to be flat.

The so-called "memory effect" is a simple case of user error in overcharging the cell. If you don't ever overcharge a Ni-Cad cell, there's no need to discharge it before recharging it again.