Rechargeable nickel-cadmium, also called Ni-Cd or NiCad, batteries have been around for a long time. They are cheap, something that has made them very popular to use in low-end consumer products. But Ni-Cd batteries have a number of shortcomings compared with newer types of rechargeable batteries.
The first nickel-cadmium battery was developed in Sweden back in 1899. The early Ni-Cd batteries had higher energy density than lead-acid batteries but they were much more expensive. The robustness of Ni-Cd batteries made them very popular. A lot of improvements have been done and Ni-Cd batteries were for a long time the best type of rechargeable batteries. They have also become much cheaper. But nowadays, the newer nickel–metal hydride and lithium-ion batteries are in most ways better than Ni-Cd batteries.
Ni-Cd batteries are often used instead of standard primary (non-rechargeable) batteries. Since they can be recharged more than thousand times, it quickly becomes much cheaper to use Ni-Cd batteries instead of buying new primary batteries. A lot of devices, such as digital cameras and cordless power tools, use special Ni-Cd batteries.
One slight problem with Ni-Cd batteries is that the cells have a voltage of 1.2 Volt. This is significantly lower than the usual 1.5 Volt. Most devices, but there are exceptions, have no problem with the lower voltage. In fact, the voltage of primary batteries decreases during discharge, often they go well below 1.2 V per cell. Ni-Cd cells on the other hand stay close the initial 1.2 Volt during discharge.
Nowadays, Ni-Cd batteries have trouble competing with the newer nickel–metal hydride and lithium-ion batteries. One reason is that cadmium is an environmental hazard and a lot of governments have restricted the use of Ni-Cd batteries. This includes the EU which has banned the use of Ni-Cd batteries in consumer products. In the US, a disposal fee has been imposed, making the batteries more expensive. But Ni-Cd batteries have a number of technical shortcomings as well.
Overcharging is less of an issue than with many other rechargeable batteries but if the battery is overcharged the battery could emit oxygen gas. In order to avoid rupture, the batteries have vents so excess gas can escape. This safety mechanism adds to the production cost.
In batteries made up of several cells, cell reversal is a potential problem. If one cell is completely discharged before the other cells in the battery, the cell could be reversed charged which damages the cell and could generate hydrogen gas which is highly explosive.
A very annoying problem with Ni-Cd batteries is the so called memory effect. If the battery is recharged before it is completely discharged, it may remember this point as when it is completely discharged. This means that the capacity of the battery is reduced. Repeated overcharging can also cause problems, some batteries start to discharge very quickly.
Despite the shortcomings, Ni-Cd batteries are used a lot, especially in the US. In EU on the other hand, they are banned, so you won’t find any Ni-Cd batteries.