Final answer:
When a higher voltage than the battery's total cell voltage is applied during charging, it pushes electric charge into the battery. Overvoltages are necessary to overcome various barriers in this process. The amount of voltage needed can vary based on several factors, including cell opposition within the battery.
Step-by-step explanation:
During the charging process, if electrical pressure, or voltage, applied to a battery is higher than the battery's total cell voltage, it forces the electric charge to flow into the battery, thus charging it. The potential energy per charge at the positive terminal of the battery dictates this voltage, analogous to water pressure in piping systems. When you apply a voltage to recharge a battery, such as the 14 V used to recharge a 12 V car battery, this includes an overvoltage to overcome barriers like activation energy required for reactions at the metal surface during charging.
The size of the voltage produced by a battery's cell is affected by various factors such as temperature, the metals used for the electrodes, and the concentration of ions in the solutions. For instance, in electrolytic processes, an overvoltage is required for the reaction to proceed. The tendency for electrons to move from one half-cell to another in a voltaic cell is termed electromotive force (emf), and if the cells within the battery oppose one another, the total emf will be reduced, as it is the algebraic sum of the individual emfs.