Might Max Battery Hydrometers are designed to detect a battery’s state of charge by sampling the electrolyte from each cell. The hydrometer contains a floating indicator that represents the density of the electrolyte. The more dense the electrolyte the higher the battery’s state of charge and vice versa. Hydrometer immediately and accurately tests battery life whether the battery is hot or cold. Help extend battery life and detects overcharge. Assists in preventing dead batteries. Compatible with all 6-12-24 volt systems.