Difference Between NiMH and NiCd

NiMH vs NiCd

NiCd (Nickel Cadmium) batteries were once the best option when looking for rechargeable batteries. They are better than lead acid batteries and come in standard sizes for most gadgets. Nowadays, NiMH (Nickel Metal Hydride) batteries are slowly replacing NiCd batteries in many applications due to a number of reasons. The biggest, and most significant, difference between NiCd and NiMH batteries is capacity. A typical NiMH battery can have a capacity that is two to three times higher than that of a typical NiCd battery. A larger capacity means longer intervals before charging or fewer spares needed for those who need a lot of power.

Although NiMH batteries have higher capacities than NiCd batteries, it would not last as long when used in low current applications like remotes and clocks. This is because of NiMH’s higher self-discharge rate of roughly 30% per month to NiCd’s 20%. The self-discharge rate is the rate at which the battery loses its capacity without any load applied. The applications mentioned above consume much less than the self-discharge rate. The appliance being powered is therefore much less of a factor with the rate at which the battery discharges.

Another major disadvantage of NiCd batteries is the memory effect it suffers from. The memory effect occurs when the battery isn’t fully discharged before charging. This causes the battery to seem like it’s lost a portion of its rated capacity. This can be fixed by a few charge/discharge cycles. On the other hand, NiMH batteries do not suffer from the problem. You can top it up any time you want. This is very convenient when preparing for trips as you can just plug the batteries in to the charger without worrying if they’ve been fully discharged.

The last major disadvantage of NiCd batteries is its content; Cadmium in particular. Cadmium is a heavy metal that has toxic effects on higher organisms. Humans who take in too much Cadmium can be subject to a variety of diseases, which can even lead to death. The problem arises when the battery fails due to overcharging or any other reason and if the battery is not disposed of properly. Although NiMH batteries also contain heavy metals, the lack of Cadmium in in its composition makes it significantly less hazardous than NiCd batteries.

Summary:

1.NiMH has greater capacities than NiCd
2.NiMH has a higher self-discharge rate than NiCd
3.NiCd suffers from memory effect while NiMH doesn’t
4.NiCd contains toxic materials while NiMH doesn’t

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