If we glance at the alternatives we’ve got for AA, C, and D cell batteries, and compare their cost, we should look at cost per kilowatt-hour. Disposable batteries square measure out and away the foremost dearly-won thanks to use energy. Depending on the type, capacity, and cost of the battery, disposables carry a price tag ranging from $400 to over $20,000 per kilowatt-hour. In contrast, the cost for using rechargeable batteries is less than $1.00 per kilowatt-hour!
- Nicad Cells
The full name of this cell type is nickel-cadmium. Nicads are made of nickel, cadmium, and potassium hydroxide in a water solution. Cadmium is a toxic material and should be recycled as such. All nicads, regardless of construction or size, produce about 1.25 volts per cell. Voltage is stable during charging and discharging, but this stability can present problems when you want to know how much energy is left in the battery.
- In Lead-Acid Battery Types,
checking the voltage will give you an idea of the cell’s state of charge. Not so with nicads, which display the same voltage from 10 percent to 90 percent of capacity.
–Sintered-Plate Nicads: This type of construction is fairly common in rechageable batteries because it costs less to manufacture. Powdered cadmium is pressed into nickel support plates. Sintered-plate cells have a calendar lifetime of about ten years under “float” charge conditions (meaning that they are kept almost completely charged at all times).
–Pocket-Plate Nicads: In this construction type, the nickel support plates are covered with perforated cavities. These weblike pockets contain cadmium, constraining it during thermal expansion and contraction. This allows fast charging, reduces loss of active materials, and makes the cell live longer.
- Nickel-Metal Hydride Cells
Compared to nicads, NMH batteries offer more capacity per cell, and no toxic chemicals. The cadmium is replaced with metal hydrides, which are environmentally benign. Nickel-metal hydride batteries have about 30 percent more energy capacity than nicads. Like the nicad chemistry, NMH cells produce 1.25 volts per cell.
- Rechargeable Alkaline Batteries
Rechargeable alkalines have some great advantages over other rechargeable chemistries, and they also have some serious problems. The advantages are that initially they have two to three times the capacity of a nicad batter; their shelf-life is as long as five years; batteries are fully charged when you buy them; they put out higher voltage output, and they contain no toxic cadmium. The disadvantages are that rechargeable alkalines lose some of their capacity—even up to 10 percent—with each cycle; because of their sharply limited number of cycles, rechargeable alkalines are significantly more expensive per cycle than nicads; and lastly, so far there is no solar charger available.