How does a rechargeable cell work?

rechargeable cell are of various types. the most common type of rechargeable cell is lead oxide cell, where sulphuric acid of certain concentration is used . during discharging process when the acid concentraton is dropped below specified level, the performance of battry decreases. by use of appropriate charging circuit, at fixed voltage not exceeding the prescribed value of current , the cell is charged until the acid level is 1.25 .