Capacity of Battery: The capacity of a cell is the quantity of electricity that it can give out during a single discharge until its terminal voltage falls to discharging volts. It is measured by the product of current in amperes and the time in hours i.e. The capacity of cell = (I d × Td) ampere-hours (or Ah) Id = Steady discharging current in amperes & Td = Time in hours for which the cell can supply current until its voltage falls to discharging volts For lead-acid cell is taken up to a point till it discharges down to 1.8 volts Application: We have, Id = 2 A Td = 15 hours Hence, The capacity of cell = (Id × Td) = 2 × 15 = 30 Ah