Primary cells are batteries that are not easily recharged after use, while secondary cells are those which can be recharged. Usually, primary cells are discarded after a single use, while secondary cells are used over and over again.
Primary cells usually lack a free-flowing electrolyte; instead, they hold the electrolyte inside solid devices called separators. Because they lack a significant quantity of liquid electrolyte, such batteries are often called dry cells. By contrast, secondary cells usually contain a liquid electrolyte, earning them the name wet cells.
After secondary cells have completely discharged, they can be recharged and used again. By pumping electric current through the cell in the opposite direction that it normally flows, the cell can be recharged for additional use.
Examples of primary cells include the types of batteries used for children’s toys, radios and similar consumer electronics products. By contrast, car batteries and standby power sources are usually secondary cells.
Because they require a liquid electrolyte, secondary cells are usually larger than primary cells. Primary cells are often less expensive than secondary cells as well, because they require fewer components and their construction is simpler. Often, secondary cells require additional maintenance, while the low cost of primary cells means that maintenance is not necessary.