The great popularity of rechargeable batteries leads to a frequently asked question:

What is the difference between NiCd and NiMH rechargeable batteries?

In short, the main differences between NiCd and NiMH batteries are related to capacity, memory effect (related to battery capacity) and environmental friendliness of the battery as such.

Also:

• Nickel Cadium (NiCd) batteries contain toxic metals and are not environmentally friendly to the extent that they would not be easily recycled or considered a sustainable solution.
• Nickel-metal hydride (NiMH) batteries have a higher energy density (higher energy storage capacity per unit mass) compared to NiCd, they have a reduced life cycle compared to NiCd batteries. Furthermore, NiMH batteries contain toxic metals and are more environmentally friendly.

Nickel Metal Hydride (NIMH) batteries have a higher capacity than Nickel Cadmium (NICd) batteries, which means they can generally power your device for longer. They also do not suffer from the memory effect, so there will be no significant reduction in capacity over time due to incomplete discharge of the battery during the charge cycle. Ultimately, NiMH batteries are much better for the environment than their NiCAD battery counterparts. However, nickel-cadmium still offers some advantages over nickel-metal hydride, such as their performance at extreme temperatures.

Here is a bit more detail about NiCd and NiMH batteries

Nickel-cadmium (NiCAD) batteries:

A standard nickel-cadmium battery consists of a nickel(III) oxide and hydroxide positive electrode plate, a cadmium negative electrode plate, a separator and a potassium hydroxide electrolyte.

Here are some of the advantages of NiCd batteries:

• NiCd batteries are relatively cheap to manufacture
• Charging is quick and easy
• Easy to store, easy to ship
• It withstands a very large number of charges
• It works great even at very low temperatures

And here are some of their disadvantages:

• Smaller capacity than some other rechargeable batteries
• Self-discharge during storage
• They contain toxic metals that are harmful to the environment

Nickel-metal hydride (NiMH) batteries

The chemical composition of a standard nickel-metal hydride battery looks like this: a nickel hydroxide positive electrode plate, a hydrogen ion negative electrode plate, a separator, and an alkaline electrolyte such as potassium hydroxide.

Several advantages of using a NIMH battery:

• Quite high capacity compared to other rechargeable batteries
• It is resistant to overcharging and overdischarging
• Extremely low battery mass
• no hazardous materials such as cadmium, mercury or lead

And here are some disadvantages:

• Relatively expensive technology
• Quickly self-discharges during storage.
• Charging is more demanding