NiCad (Nickel-Cadmium) and NiMH (Nickel-Metal Hydride) are among the most commonly used batteries for smaller home electronics, in no small part because they are both excellent for rechargeable applications. However, there are several important differences between the two, and its important to be aware of these differences when choosing the right battery for your project.
NiCad batteries can withstand much higher rates of charge and discharge than NiMH batteries. Simply put, you can charge NiCad batteries much faster without damaging them, and they can discharge at rates greater than the 1.5- to 2-amps that are about the maximum that most NiMH batteries can handle. This is why NiCad batteries are often used in power tools, where greater amounts of power may occasionally be needed.
NiCad batteries have lower self-discharge rates than NiMH batteries. Self-discharge is when batteries lose power during periods of non-use, and all batteries suffer from it, to some extent. However, while NiMH batteries can have self-discharge rates up to 25 to 30 percent per month, NiCad batteries are often around 10 to 15 percent.
Where NiCad batteries fall short of NiMH is in the amount of energy that can be stored. Though NiMH batteries cannot charge or discharge as fast as their older counterparts, they can store much more energy in the same amount of space. The energy density of a NiMH battery can be over 300 watt-hours per liter, while NiCads can be as low as 50 Wh/L.
Which to Choose?
If your project will need varying amounts of power, and will need a battery that can provide greater amounts of power over shorter periods of time, NiCad is the way to go. However, if your project has lower power needs, but will need to draw power consistently and for long periods of time, NiMH is the way to go. And if you’re torn between the two, keep this in mind: NiMH batteries are more cost-effective, giving more power for your buck.