Sulphuric acid is generated during the charging of battery plates in the plate formation jars. Dilute solution of sulphuric acid is used as an electrolyte in the formation jars, in which the plates are arranged as cathodes and anodes. External electrical potential is applied to the series of cathodes and anodes to carry out the charging operation. Electrolytic reactions taking place during the charging operation result in formation of sulphuric acid. Thus, the concentration of sulphuric acid in the formation jars, which is initially approx.4%, ( Sp. Gravity = 1.030 ), increases up to 6-8% ( Sp. Gravity of 1.060 ). In order to maintain the acid concentration at 4% level, some quantity of acid is removed from each jar and the reduced volume is made up by addition of DM water into every jar. This acid removal is done after every charging cycle of approx. 35 hours.