One of the difficult things to understand about a battery is 'memory effect'. It occurs only in the Ni/Cd cell. Thus, the charger for Ni/Cd cell is designed to recharge the cell after full discharge. In general, the cycle-life of the cell gets longer when the cell repeats shallow charged or discharged. That is, just like a human being, you can use a battery longer than the expected life span of it if you use it properly.

However, it is a different story with a battery made of nickel. In the Ni/Cd battery, OH is attached to and detached from NiOOH used as an active material. This is the way of delivering electric charges and appears as an electric flow, that is, charge and discharge.

If you repeat shallow charge-discharge, NiOOH forms a solid solution and this formation is a irreversible reaction so that you can not use the rest capacity of the cell.

Like this, a phenomenon as a battery remembers the limit capacity of it is called ' memory effect'. Therefore, when using a cell employed nickel electrode, it is a better way to use the cell to the end of its capacity (above the lower limit of discharge) and charge it to the full repeatedly.

There is, however, no 'memory effect' in the Li-ion cell so that the life span of a Li-ion cell is not influenced even though the battery is discharged and recharged repeatedly at all times. On the contrary, you can get the effect of lengthening the life span of the battery if you use a little and recharge it again and over again. With this reason, more people prefer to the Li-ion cell and the demand is expanding even though its price is higher than that of the nickel battery.