H ELECTRICITY
H01 ELECTRIC ELEMENTS
H01M PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
10/00 Secondary cells; Manufacture thereof
H01M10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
H01M10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte