TopTechnical DictionaryBattery capacity

Battery capacity

Batteries are types of galvanic cells capable of multiple storage of energy in the form of an electrical charge. They are used in almost every sphere of life. Regardless of the type, structure and dimensions, each battery has several basic parameters. One of the main ones is the battery capacity expressed in Ah (amp-hours).


The battery capacity is the product of current and time. In a great simplification it can be said that capacity determines the maximum product of the current output of the battery at a given time. Of course, depending on the technology and design, the components of this product are strictly defined. Please note that this parameter does not indicate how much power the battery can store. The unit Wh (watt-hour) is used for this purpose, which characterises it better and for this reason it is now used more often.




Capacity measurement is done differently for each type of battery. This is due to the difference in chemical processes taking place inside it. The capacity is determined by measuring the time and current of battery discharge within a specific voltage range at its terminals. The key value here is the range of the operating voltage, and more precisely the permissible minimum voltage of a discharged battery and the maximum voltage of a charged battery at which it is not permanently damaged.
It should be noted here that these two voltages may have different values depending on the value of the discharge current and the charging current. The maximum current is also strictly defined by the manufacturer.


In addition, the capacity value depends on the temperature and the number of loading/unloading cycles already completed.


For example, in the case of AGM lead-acid batteries, manufacturers specify the rated capacity of the battery for a discharge time of 20 h at 20°C.
The capacity for these batteries has a different value depending on the load current and operating temperature. The exact value can generally be determined from the data sheets, in which the manufacturers include the discharge characteristics.


Battery capacity is not a constant value. Even an unused battery loses its parameters after some time and its capacity decreases. Factors that affect its life, i.e. its capacity, are given in the specification sheets. The main ones include:

  • operating temperature in ranges other than those specified by the manufacturer,
  • number of charge/discharge cycles completed,
  • discharging below the permitted voltage,
  • battery overcharge,
  • discharging with too high currents.