Primary and secondary cells
Some electrical cells, once their potential energy has all been changed to electricity and used up, should be thrown away. They are of no use anymore. These are called as primary cells.
Other kinds of cells, like lead and acid unit depicted above, can get their chemical energy back again. This type of a cell is called as secondary cell.
Primary cells include ones you put in a flashlight, in a transistor radio, and in several other consumer devices. They use dry electrolyte pastes along with the metal electrodes. They go by names like zinc-carbon cell, dry cell, alkaline cell, and others. Go to the department store and find the panel of batteries, and you will see various sizes and types of primary cells, like AAA batteries, D batteries, camera batteries, and watch batteries. You should know that these things are cells, not true batteries. This is a example of a misnomer which has gotten so widespread which store clerks might look at you funny if you ask for the couple of cells. You will also see real batteries, like the little 9-V transistor batteries and the large 6-V lantern batteries.
Secondary cells can be found increasingly in consumer stores. Nickel-cad- mium cells are the most common. They are available in some of the same sizes as nonrechargeable dry cells. The common sizes are AA, C, and D. These cost several times as much as anormal dry cells, and a charging unit costs a few dollars. But if you take care of them, these rechargeable cells can be taken in use hundreds of times and will pay for them.
The battery in the car is made from secondary cells which connected in the series. These cells recharge from the alternator or from the outside charging unit. This battery has cells like the one in Figure. It is dangerous to short-circuit the terminals of such a battery, as the acid can boil out and burn your skin and eyes.