In electricity, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy.
There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes; from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers.
A battery is a device that converts chemical energy directly to electrical energy. It consists ofa number of voltaic cells; each voltaic cell consists of two half-cells connected in series by a conductive electrolyte containing anions and cations. One half-cell includes an electrolyte and the electrode to which anions migrate, i.e., the anode or negative electrode; the other half-cell includes an electrolyte and the electrode to which cations migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery, cations are reduced at the cathode, while anions are oxidized at the anode. The electrodes do not touch each other but are electrically connected by the electrolyte. Some cells use two half-cells with different electrolytes. A separator between half-cells allows ions to flow, but prevents mixing of the electrolytes.
Each half-cell has an electromotive force (EMF) determined by its ability to drive electric current from the interior to the exterior of the cell. The net EMF of the cell is the difference between the EMFs of its half-cells, as first recognized by Volta. Therefore, if the electrodes have EMFs E 1 and E 2 , then the net EMF is E 2 -E in other words, the net EMF is the difference between the reduction potentials of the half-reactions. The electrical driving force or ΔV bat 1 across the terminals of a cell is known as the terminal voltage (difference) and is measured in volts.