A battery is a component that stores and provides power to electrical devices. When battery is connected to an external circuit, electrons flow through the negative terminal, the anode, and deliver energy to the electrical device.
There are two primary battery types: primary and secondary. Primary batteries can only be discharged once and must be discarded after use. Alkaline batteries, typically used to power power flashlights and other portable electronics are primary batteries. Secondary batteries can be discharged and recharged multiple times by applying an electric current in the reverse direction. Lithium-ion batteries are secondary batteries, and typically power smartphones and laptops.
Because of the large amount of handheld devices that require battery power, small alkaline batteries are the most common type. They are used to power most portable test equipment like multimeters, voltmeters and IR thermometers.