Electric Batteries: Principles, Types, Performance

Definition and basic operation of batteries

An electric battery is a power source made of one or more electrochemical cells with external connections, used to supply electricity to devices. When operating, the battery’s positive terminal acts as the cathode and the negative terminal as the anode; the negative terminal is the source of electrons. Connecting the battery to an external load causes electrons to flow through the circuit, driving a redox reaction inside the cells as ions move, converting chemical energy into electrical energy delivered to the outside circuit. Batteries are built from voltaic (electrochemical) cells, each containing two half-cells and an electrolyte that allows ion movement between electrodes. The cathode and anode undergo reduction and oxidation respectively, producing an electromotive force (emf) measured in volts. The terminal voltage depends on whether the battery is charging or discharging and is affected by internal resistance: during discharge it is lower than the open-circuit voltage (emf), while during charging it can exceed it. Batteries can be single-use (primary) or rechargeable (secondary), with secondary batteries restoring their electrode chemistry when recharged by applying current.

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Cathode and anode roles in electron flow

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