The Standard Float Type Hydrometer is a large size float type tester with a glass tube and a color-coded float for easy reading and identification. This product is know for its precise reading of battery charge condition and it features a hexagon tip that prevents undesired rolling when not in use.. The prod A battery hydrometer is the ideal product for testing the state of charge in a given battery cell. The hydrometer is placed in the cell and produces a reading by measuring the density of electrolyte inside the battery cell.