Ideal battery capacity

The battery capacity is a measure of the amount of charge or energy stored in the battery. The fundamental units of battery capacity is coulombs (C), although a more common and useful unit is Amp-hrs (Ah) (amps = C/time, so Ah = C/time(sec) x time (hrs)). The battery capacity in Ah can be ideally calculated from the weight/volume or number of moles of materials of the electrode and electrolyte (if it is an active component in the redox reactions) in the battery. The ideal battery capacity under equilibrium conditions (which can differ substantially from the “real” battery capacity under load) is calculated by from the moles of available reactants, from which the moles of electrons can be determined. Using Faraday’s constant, which gives the number of Coulombs for a mole of electrons (F = 96,484.56 C/mol), the total available coulombs (charge) can be determined for the battery. Since the battery capacity, when described in Ah is a measure of the total stored coulombs (Amps are C/sec), then the battery capacity can be determined by the equation:

Since the primary function of a battery is to store electrical energy rather than electrical charge, the energy storage of a battery is also an essential parameter. A simple way to determine the energy storage capacity of the battery is to multiply the Ah capacity by the nominal battery voltage, such that: