To prevent lowering of terminal voltage at the time of immediately usable discharge by making a larger quantity of tin dioxide than at the inside of active material layer exist in a crack part reaching the surface of the active material layer and the surface of an electrode plate with a grid surface part in which a positive electrode plate is exposed.

By making a larger quantity of tin dioxide than at the inside of an active material layer exist in a crack part reaching the surface part of the active material layer and the surface of an electrode plate with a grid surface part in which a positive electrode plate is exposed, the conductivity of the grid and the active material is performed by tin dioxide (SnO2) and lowering of terminal voltage is eliminated. After the positive electrode plate in which a tank is formed according to a conventional method, for instance, is washed in flowing water for about 3 to 30 minutes, an immersion processing is performed for the positive electrode plate in 0.5 to 2.0% aqueous solution, for instance, of stannous oxide (SnO) or stannous sulfate (SnSO4) for a minute and the positive electrode plate is dried at 120°C for 15 minutes. This positive electrode plate processed is higher in terminal voltage at the time of immediately usable discharge as compared with a positive electrode plate which is only washed in water for 30 minutes and is dried as it is.