Types of Cells

Electrical cells can be broadly divided into several categories, including PRIMARY cells, SECONDARY cells, and FUEL cells.

A PRIMARY cell cannot be recharged once its chemical reaction has run its course -- it is designed to be used only once and then discarded. Ordinary dry cells and alkaline cells are common examples. Primary cells are low-cost and convenient to use, but they are not well suited to applications that draw heavy, sustained currents (loads).

SECONDARY cells, by contrast, ARE rechargeable and can be reused many times, because the chemical reaction that powers them is REVERSIBLE (running the reaction backward, by forcing current into the cell, restores the original chemicals). Lead-acid cells are the classic example, and are used widely in vehicles and other applications that need to deliver high load currents (such as starting an engine). Solar cells, which convert solar (light) energy into electrical energy, are also classed as a type of secondary/rechargeable-in-effect cell in this scheme, since they can keep supplying energy as long as light continues to fall on them. …