An alkaline battery is a type of primary battery where the electrolyte has a pH value above 7. Typically these batteries derive energy from the reaction between zinc metal and manganese dioxide.
Size comparison of alkaline batteries (left to right): C, AA, AAA, N, PP3 (9-volt).
Thomas Edison's nickel–iron batteries manufactured under the "Exide" brand, originally developed in 1901 by Thomas Edison use a potassium hydroxide electrolyte.
A primary battery or primary cell is a battery that is designed to be used once and discarded, and not recharged with electricity and reused like a secondary cell. In general, the electrochemical reaction occurring in the cell is not reversible, rendering the cell unrechargeable. As a primary cell is used, chemical reactions in the battery use up the chemicals that generate the power; when they are gone, the battery stops producing electricity. In contrast, in a secondary cell, the reaction can be reversed by running a current into the cell with a battery charger to recharge it, regenerating the chemical reactants. Primary cells are made in a range of standard sizes to power small household appliances such as flashlights and portable radios.
A variety of standard sizes of primary cells. From left: 4.5V multicell battery, D, C, AA, AAA, AAAA, A23, 9V multicell battery, (top) LR44, (bottom) CR2032